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. Client's Name and Address: Provide the client's name and address as it appears in payment system. 2. Date: Enter the date that the DSHS 18-398 is filled out. 3. If you have an overpayment, we'll send you a decision letter. It will say how much you owe. 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. Please call 1-800-772-1772 or your local field office and we may be able to process your waiver request quickly over the phone.