Dear When I received your letter of [date] with my attached check marked "insufficient funds", I called my bank immediately. The gentleman with whom I spoke, [name] , discovered that the bank had failed to credit my account with the substantial deposit I had made several days earlier. The bank has assured me that they will be sending you a formal letter of apology for their error. Enclosed is my check in the amount of $___ to replace the dishonored one you have returned.