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.You have to tell your credit or debit card company about any error you're disputing within 60 days of when the first statement with the charge was sent to you. Members receiving overpayment letters must respond promptly, as they are given four weeks to do so. The salary overpayment resulted because . Overpayments happen for various reasons. For example, DES may not budget your correct income or resources.