People are being warned not to bin a letter from Barclaycard if it lands on your mat this week - as it could contain a cheque for up to £300.
Current and former customers of the credit card company are being sent refunds, according to MoneySavingExpert.com, with some revealing they have had up to £300.
Barclaycard says the average refund amount is £70.
Refunds are for incorrect interest and fees charged to some customers. There could also be interest added on top as well as a deduction for income tax.
Former customers are likely to get a cheque or transfer while current customers may see the money returned to their accounts.
Everyone affected will get a letter or email telling them the money is there - so MSE says you should check the contact details Barclaycard has for you are correct.
They say: "You can ensure this by logging into your online banking via the app or the website then selecting 'your contact details', or by phoning customer service on 0800 151 0900.
"If you think you're affected you can also contact the lender to check by calling the same number above. Alternatively, you can join an online chat through the Barclaycard app."
The money is being refunded to some customers who took out repayment plans before 2018 and were overcharged.
Some customers on repayment plans, who fell behind, were charged default fees and interest incorrectly.
A Barclaycard spokesman told MSE that it "apologises unreservedly to those customers" and that it "has taken, and continues to take, significant steps" to review and improve its "systems, processes and training".
Last year HSBC took similar action with compensation for customers who were in arrears between 2010 and 2019.
