This brief but important letter notifies a customer that he or she has overpaid you. It can serve as a very good customer relations letter.In this article, we discuss how to write a refund request letter, what to include in the letter, and provide a sample refund request letter. Ms. Cartwright and her 3-year-old daughter were eligible for MC with no SOC. The salary overpayment resulted because . Use this sample letter. Send your letter so that it reaches the issuer within 60 days after the first bill with the error was sent to you. If we have identified an overpayment and request a refund, please mail the check along with a copy of the overpayment request letter we sent you. In Benefit Overpayment Services, you can make a payment, view past payments, and set up an installment agreement to make monthly payments. You have to tell your credit or debit card company about any error you're disputing within 60 days of when the first statement with the charge was sent to you.