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.If you were overpaid, you will receive a written notice in the mail. The salary overpayment resulted because . Establish paternity; Establish and enforce support and medical orders; Collect support payments on behalf of parents to whom support is owed, known as obligees. Our document template is designed to make the process of writing an "Inform a Customer of an Overpayment" letter quick, easy, and stress-free. What Is Overpayment? We have identified the following overpayment and are in good faith voluntarily refunding all monies collected in error.