Dear _______________

On ______________ (date) this office mailed to you a check of the amount of ___________ as per your _______________ (date) of invoice.

After reviewing your file, I realized that this account had been paid in full on ____________ (date). I am enclosing a Photostat of our cancelled check __________ in the amount of _____________ (amount).

I would appreciate it if you would reimburse this office for the duplicate payment. I apologize for any inconvenience this error has caused.

Thank you for your prompt attention to this matter.