A stop payment may be requested for checks not received within three weeks. Overpayments are Medicare funds that you or a beneficiary has received in excess of the amount allowed payable under the Medicare statute and regulations.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 . We have identified the following overpayment and are in good faith voluntarily refunding all monies collected in error.