For the open invoice in the Payment column, enter how much of the credit you want to apply. If you were overpaid, you will receive a written notice in the mail.Discover how our refund letter to customer template can enhance satisfaction and loyalty, with professional tips for seamless communication. It's literally on Discover's site that most cards will issue a statement credit in the case of an overpayment. When you overpay your credit card, extra funds generally remain as a credit on your account. But there are more options you may consider. If you receive a letter asking for missing information or documentation to support what you claimed on your return, it doesn't mean you did anything wrong. 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.