Farmers sent letters by the Rural Payments Agency demanding repayments should check whether they really do owe money before they pay.
Experts have warned the agency is still making errors over how much farmers owe, despite being criticised by the National Audit Office in October for asking for incorrect sums to be returned.
Chris Windle, of chartered surveyors Windle Beech Winthrop, said clients had received incorrect repayment letters.
“When we asked the RPA for evidence of overpayments, we realised a huge number of errors were being made,” he said.
“One chap was asked for £30,000 back, when he didn’t actually owe anything. That was in early summer, but there are still mistakes being made.”
In the latest incident, one of his clients had been asked to repay £2000, even though the money was rightfully his, Mr Windle said.
“My advice is if you receive an overpayment letter and the calculations are there, make sure you check them or get them checked by a professional,” he added.
An RPA spokeswoman said 340 of about 1700 farmers had successfully queried overpayment calculations.
“Identifying and resolving overpayments is a complex process,” she added. “On request the RPA can give farmers further information on how the debt has arisen.”