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.Tell them that they have "overpaid" you. Then ask them to ring you for details. This template informs a customer about a credit adjustment due to overpayment, returned items or as a result of resolving a dispute. The salary overpayment resulted because . Appeal the Overpayment. The first part of the appeal is to forget about the 60 day window. Discover how our refund letter to customer template can enhance satisfaction and loyalty, with professional tips for seamless communication.