Dear　　When I received your letter of  [date]  with my check attached marked "insufficient funds"， I called my bank immediately.

　　The gentleman I spoke with，     [name]    ， discovered that the bank had failed to credit my account with a substantial deposit I had made several days prior.

　　The bank has assured me that they will be sending you a formal letter of apology for their error.  Attached is my check in the amount of $         to replace the dishonored one you have returned.