Dear Valued Customer,
We owe you an explanation about what happened in our accounting department. I hope that this letter will help to address the problem.
I know that you understand that it takes sometime for us to determine exactly what happened. That is why we are sorry for our late response.
Fortunately, your payment was received promptly. However, it was credited to an account that has a similar name to yours. Therefore, we begin sending you our standard notices requesting payment in accordance to our payment policy. Even after the posting error was retrieved, our accounting department failed to inform our credit department. That is why you continued to receive conformity demanding payment.
I know how infuriating this to you and I am sorry for taking it so long to resolve the problem. Even though there is a procedure to our firm to impede this type of mistake from occurring. We are strengthening this procedure.
You have been our valued customer for a long time and we are truly happy to serve you. We will do our best so that a problem like this will not arise.