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.Our document template is designed to make the process of writing an "Inform a Customer of an Overpayment" letter quick, easy, and stress-free. The salary overpayment resulted because . 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. Overpayment Information. If you have received an overpayment notice from DETR, you may be required to repay the excess amount. This memorandum serves as notification of an overpayment of wages that you received and the subsequent repayment that is your responsibility.