Apology For Mistaken Past-due Notice / Accounting Error

Dear Valued Customer,

I wrote a letter to extend my deepest apology to you. I conducted thorough examination of our records and I found out that the past due notices that we sent to you were incorrect. The error has been resolved and your current balance is $ ________.

I hope you will give me the opportunity to explain the situation. Your payment was received promptly. However, due to an error it was not detected by the system that you are paid already. Therefore, you received notices requesting for your payment. After the deadline for the payment, our credit department generates Past Due notices. Please be informed that this problem was settled.

I apologize for the inconvenience. We are truly happy to inform you that we are implementing measures to impede this case to happen again. You have been a loyal customer and we appreciate your existence.

If you have more queries about this matter, just contact us in your most convenient time. I am looking forward to serve you in the future. 

Sincerely Yours, 

(Name)