The Tax Office holds unclaimed property tax overpayments made within the last three years and outstanding (uncashed) refund checks. 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. The salary overpayment resulted because . Tell them that they have "overpaid" you. Then ask them to ring you for details. Tthe Social Security Administration is demanding people return overpayments that, in some cases, were the government's fault.