A carer who says he was “dragged through the courts” and had to sell his home to pay back almost £20,000 in benefit overpayments is fighting to clear his name after the Department for Work and Pensions (DWP) acknowledged he made an innocent mistake.

George Henderson, 64, said he made a gain of just 30p a week while claiming carer’s allowance for his son John, who has learning difficulties and is addicted to heroin. He now costs the Treasury £1,000 a month more in benefits, having become homeless and too unwell to work.

Henderson said he was left suicidal after being prosecuted by the DWP, which accused him of fraudulently claiming the benefit for six years while he was caring for John, who is now 42.

He wrongly ticked a box saying he was unemployed while filling in the “tricky” application form for carer’s allowance in 2010. “I thought they were asking about John,” he told the Guardian.

The DWP has records of him working as a taxi driver since 2002, earning about £7.50 an hour. Yet it took more than six years for anyone at the department to tell him he was claiming the benefit incorrectly.

By that point he had claimed £19,506.20 – about £60 a week. The DWP not only wanted it all back but also prosecuted him for fraud. Investigators said he had lied about having a job and had ignored annual letters reminding him to report any changes in circumstances.

He protested his innocence but was found guilty. In 2018, a judge at Preston crown court gave him a 32-week suspended sentence and ordered him to wear an electronic tag for 16 weeks.

Never in trouble with the law before, Henderson found it humiliating having the tag fitted and suddenly having a 9pm curfew. “My stomach was churning watching them putting it on,” he said. “I just felt helpless, embarrassed, degraded … I’d been dragged through the courts like a criminal, and I’m not.”

Afterwards, he received letters from the DWP every three weeks demanding he sell his two-bed former council flat to pay the debt or face a seven-month jail term, he said.

Henderson eventually sold the property for £115,000, and after paying off his mortgage and the DWP he was left with just £6,000. “It breaks my heart,” he said. “I’ve been back and looked at [the house] twice and I’ve actually broke down and cried.”

His mental health deteriorated to the point that he attempted to kill himself and became seriously unwell. “I’d lost four stone. You could actually see my ribcage.”

Henderson is one of a number of carers the Guardian has spoken to after exposing how people looking after disabled, frail or ill relatives are being forced to repay huge sums to the government and threatened with criminal prosecution after unwittingly breaching earnings rules by just a few pounds a week.

The government is facing calls to overhaul the system after the Guardian revealed that tens of thousands of unpaid carers are facing severe fines, some over £20,000, for relatively modest and unintentional breaches of rules branded “cruel and nonsensical”.

John, Henderson’s middle child, was born healthy but lost most of his hearing and developed disabilities after contracting measles aged three. He was unable to manage living independently as an adult, particularly after becoming addicted to heroin, and so moved in with his father.

Initially, John was claiming disability benefits worth about £60 a week. But Henderson soon realised that John’s drug dealers would wait by the cashpoint each week when he was paid, taking his money off him for heroin.

Henderson claimed that in 2010 a DWP official came to the house to assess John and they discussed the pros and cons of claiming carer’s allowance instead.

The new benefit was worth 30p a week more but meant Henderson could receive the money into his bank account and pay it to his son as a daily allowance, with the aim of stopping it being taken by the heroin dealers.

After his conviction in 2017, Henderson tried and failed to appeal. He was left homeless and had to be housed by the local council in sheltered accommodation, at a cost to the public purse. Too unwell to work, he now relies on universal credit, receiving £1,300 a month to cover his housing and living costs.

“Believe it or not, when I moved in I couldn’t get in and out of the bath because I’ve got two hip replacements and I’ve got a serious spinal condition. So it cost them £7,000 to put in a wet room. It’s costing them the universal credit. It’s absolutely ludicrous. It’s actually cost the taxpayer or the government money by doing this,” he said.

Recently, Henderson decided to try to clear his name and wrote to Mel Stride, the work and pensions secretary. Last month he received a letter from the DWP apologising for his ordeal but refusing to give him the money back.

The letter said: “The appeal conceded that you were a convincing and credible witness [and] it was more probable than not that you were telling the truth and that the false declaration was an innocent mistake.”

It went on: “I am so sorry that you feel that experiences with DWP have contributed to your financial problems, severe emotional trauma and mental health.”

Henderson refuses to accept the apology. “It’s not addressing what I need addressed,” he said. “Why did it take six years to find that I ticked the box incorrectly? Why not in the first year? Then it would be acceptable. I would have been able to pay the first year, I made a mistake.”

A DWP spokesperson said: “We are committed to fairly supporting all those who need the welfare system, while fulfilling our duty to treating taxpayers’ money responsibly.

“Claimants have a responsibility to inform DWP of any changes in their circumstances that could impact their award, and it is right that we recover taxpayers’ money when this has not occurred. We will work with those who need support with their repayment terms whilst protecting the public purse.”