Unpaid carers must repay more than £250 million after many were unknowingly overpaid their allowance, new figures show.
The government is seeking to recover money from more than 134,000 carers.
Carer's Allowance must be repaid in full if a strict earnings limit is exceeded by even a few pence.
The Department for Work and Pensions (DWP) said it was "progressing an enhanced notification strategy" to alert carers to overpayments.
Wren Seaward, a full-time carer for her husband John who relies on a wheelchair because of severe osteoarthritis, must pay back £245 a month after unwittingly receiving £5,000 in overpayments.
This has brought a "considerable financial strain" and "makes many of the things we could do in the home to make John's life easier... very difficult to access", she told the OceanNewsUK.
The couple admit missing DWP letters reminding them to report any changes in circumstances, but say they became overwhelmed with correspondence following the death of their daughter in a car crash.
Unpaid carers who provide care for someone for more than 35 hours a week are entitled to receive the Carer's Allowance.
However they are only eligible if they earn less than £151 per week after tax. If this is exceeded following a change in circumstances - such as working overtime or a modest pay rise - they are no longer eligible and have to repay any allowance received in full.
The latest figures were released by the DWP after a parliamentary question from Labour MP Sir Stephen Timms.
The datashows more than twice as many women are in debt because of overpayments, roughly in line with the proportion that receive Carer's Allowance.
The DWP has previously said that "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".
But carers have told the OceanNewsUK they were unaware they had exceeded the threshold until being informed years later, by which time the sums had run into the thousands.
'Not enough progress'
In 2019, a report by the Work and Pensions Committee warned carers could be "heavily penalised for making honest mistakes", as errors in claims were not being spotted quickly enough by the DWP due to "problems with its systems" and "staff shortages".
At the time, the government said it believed it was "well on the way" to fixing those problems and limiting overpayments.
On Thursday, the Work and Pensions Committee warned there has "not been progress" in limiting the impact of the problems raised five years ago, and called on the DWP to "improve urgently" how it monitors and communicates allowance overpayments.
Sir Stephen, who chairs the committee, said the government "has known for years" about the issues, but had "just allowed many unpaid carers to unwittingly rack up unmanageable levels of debt".
"The DWP must now move without delay to get a grip of the problem and ensure carers are no longer subjected to the distress that such overpayments can cause," he said.
Last month two former DWP ministers - Conservative MP Sir Iain Duncan Smith and the Liberal Democrat pensions minister during the coalition government, Sir Steve Webb - called on the government to pause its demands for repayments of large sums of money.
A report by the Department for Work and Pensions (DWP) published last week said, of more than 1,000 carers surveyed, 3% had to make repayments after changes in circumstances meant that they received the benefit in error.
Emily Holzhausen from Carers UK, said carers are often "shocked and horrified" when they find out they have been overpaid.
"It's devastating for their mental health, and feels really tough paying that back", she said.
Karina Moon, whose daughter Amber requires round-the-clock care, owes £11,000 after earning slightly over the claim limit at her part-time supermarket job.
She has been paying back £60 a month for the last four years, and will continue paying for another 11.
"It takes money out of our income", she said, "it's money that would help me run the car, help pay bills, put food on the table".
Meanwhile Gina Price, from Carmarthenshire in south-west Wales, cared for her dad while working part-time at a petrol station. She said she would sometimes agree to work an extra shift, but would do fewer other weeks. This way, she believed she would remain under the earnings threshold to qualify for the benefit.
She now owes the DWP around £7,000 in overpayments, and said the debt was a "huge blow".
It is "a big debt by anyone's standards", let alone someone working part time, she added.
Liberal Democrat leader Sir Ed Davey, a carer himself, has called for these debts to be cancelled.
"It's just unbelievable" that carers are being forced to repay as a result of the "government's own incompetence", he told the OceanNewsUK.
"People work hard, they pay their taxes, they look after their loved ones, the government should be incentivising work," he said.
The Department for Work and Pensions said the total amount of Carer's Allowance overpayments "includes historical debts which the department is seeking to recover".
"In comparison, Carer's Allowance expenditure is forecast to be £4.2 billion this year alone," it said.
"Carers across the UK are unsung heroes who make a huge difference to someone else's life, and we have increased Carer's Allowance by almost £1,500 since 2010," the department added.
