Simply replace the unfilled areas such as "" and "[date]" with your information.
After reading your letter of [date], I can thoroughly understand why you are running out of patience.
While it would be easy to place the blame on our computer, this poor fellow has received enough abuse since joining our firm. After all, he only follows the orders that are given to him. Please accept my apology for the delay in refunding your money for [problem].
Our bookkeeping department has been instructed to issue a check to you at once, which you should be receiving it shortly.
I am grateful that your letter was brought to my attention and I appreciate your perseverance in settling this matter. Once again, I am very sorry for the inconvenience this has