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.This memorandum serves as notification of an overpayment of wages that you received and the subsequent repayment that is your responsibility. The salary overpayment resulted because . A refund letter to a customer should be structured to convey the necessary information clearly, empathetically, and respectfully. We have identified the following overpayment and are in good faith voluntarily refunding all monies collected in error. How do I apply for Child Support Services? You can complete the application at your local CSS office or apply online.