Maths teacher John Hammond was a few weeks into his job at a new school, chatting to colleagues in the staff room during lunch break.
He decided to check his banking app to make sure his first month's wages had arrived, but instead discovered £20,000 had been taken by the Child Maintenance Service (CMS).
"I was so shocked that I couldn't stop shaking," he says. "Other teachers could see something was wrong and asked what was the matter."
Hammond's children were 25 and 28, and his child support arrangement had finished more than a decade previously.
"I was convinced that it was a scam," says the 56-year-old from Peterborough.
More than 30 parents have told BBC Your Voice they've experienced miscalculated child maintenance arrears, money wrongly taken from wages or bank accounts and lengthy court battles with the CMS.
As in Hammond's case, the BBC has found many of these reported issues are connected to child support arrangements concluded many years or even decades ago.
The CMS replaced the Child Support Agency (CSA) in 2012. Its job is to ensure a child's living costs are paid when one of their parents does not live with them.
It uses a formula to work out how much a parent should pay. If parents cannot arrange payments privately the CMS can take the money from wages, bank accounts, benefits or pensions.
It also has the power to recover arrears if parents fall behind with payments.
The experiences shared with the BBC mirror concerns about the CMS raised with the government after parents told a House of Lords report money had been taken "inappropriately" when they were "trying to comply".
The Department for Work and Pensions (DWP), which runs the CMS, did not address the experiences of John Hammond and other individual cases, or explain why in some cases money was taken wrongly from bank accounts. It said it tries to arrange voluntary arrears payments and "enforcement measures are only taken if parents continue not to pay".
John Hammond believes his ordeal started in September 2002 when he received a letter from the now-defunct CSA which said he owed £947, but it did not intend to collect it at the request of his ex-wife. He believed he no longer owed any child maintenance.
But in 2019 he got a letter from the CMS saying he owed almost £19,000.
"I was in complete shock," says Hammond, who disputed the demand, sending copies of the letters to the CMS.
"You phone up and explain everything," he says. "They tell you they can't access your account or that the computer says something different. It felt like banging your head against a wall."
In correspondence seen by the BBC, the DWP said it was "unable to ascertain why" Hammond was told he owed £19,000.
But while Hammond's challenge was ongoing the CMS obtained interim and final lump sum deduction orders and in December 2020 took £19,269 from his bank account.
Hammond won his appeal a year later and a county court judge ordered the full sum to be returned and awarded him £8,000 in legal costs.
He had spent £14,055 on legal fees and says he remains more than £6,000 out of pocket.
"Even when you're proved right it doesn't feel like justice," Hammond says. "It just feels like you've survived it."
Richard George, 63, discovered £18,800 had been taken from his bank by the CMS.
"I won't forget it, how I felt - it triggered in me the most horrendous adrenaline shock," says George, a founder director of a fintech startup company from Devon.
"It's a bit like your last money, everything you've got left, is taken by a scammer. That's what I thought had happened."
George's ordeal dates back to 2016 when an appeal tribunal overturned a CSA decision against him, effectively writing off more than £16,000 in arrears.
Richard says he believed the case, relating to maintenance for one of his children, had ended, particularly as the CSA had been wound down.
It wasn't until late 2019 that the CMS contacted him unexpectedly and removed £18,800 from his bank account.
George later discovered that CMS correspondence intended for him had been sent to the wrong address for several years, despite letters being returned undelivered and him repeatedly confirming his details by phone.
It took until 2023 for the CMS to accept the arrears should never have been carried over.
"They paid the money back in the end - everything taken since 2019, including the collection fees," George says, "but by then the damage had already been done."
Concerns about the CMS were raised with government in a House of Lords report entitled Reforming the Child Maintenance Service in October 2025.
One parent described enforcement as "random, abusive and unregulated".
"It punishes the wrong people and ignores real avoidance," the report stated.
In a separate issue to the enforcement errors experienced by John and Richard, the Lords report found the calculation formula the CMS uses to decide how much a parent should pay has been in place for more than two decades and "is neither fair nor transparent".
"We believe it is outdated and does not reflect the structure of modern families," the report said.
The government has committed to conducting a review into the CMS' calculation model and said it was considering the report's recommendations as part of an ongoing review.
The CMS manages 800,000 arrangements for 720,000 paying parents, according to DWP figures for 2025.
It sets payment arrangements based on a paying parent's income and "assessment accuracy rates are consistently close to 100%", the DWP says.
If parents dispute a decision it can be appealed and an independent tribunal will decide if it should be changed, a DWP spokesperson added.
Parents the BBC spoke to say they do not dispute paying child maintenance, but they do dispute the accuracy of calculations and enforcement action being taken before appeals were resolved.
In 2025 the CMS received 92,700 requests from parents to reconsider a decision and in 21,400 cases the original decision was found to be incorrect or the parent supplied more information which changed the decision. This means almost a quarter of decisions were changed.
The DWP told the BBC it does not publish data for the number of appeals against arrears notices, bank deductions or other enforcement.
Abigail Wood, chief executive at Gingerbread, a charity for single parent families, said it had campaigned for a reform of the CMS as it was "failing parents and children alike".
"We welcome the proposed changes, but the DWP needs to go further and faster to ensure a fair and functional system."
Michelle Counley from the National Association for Child Support Action (NACSA) says if the CMS worked with both parents together "many disputes could be resolved early, before figures are imposed and enforcement kicks in". She called for "serious investment and a joined‑up way of working".
Hammond and George were among parents who told BBC Your Voice they want to see an overhaul of the CMS so mistakes like this don't happen again.
"Getting the money back didn't feel like a victory," says Hammond. "It was simply the end of a long fight to recover money that CMS had no right to take in the first place."
George says although he also got his money back, "it came after years of fighting, and it didn't undo the impact it had on my health, my work or my life."
Additional reporting by Will Dahlgreen.
