Dear Mr. Sandler,
I understand that you have been given the wrong product by our sales clerk from one of our stores. I know this letter has taken so long in coming but it was brought to my attention only recently and I took a corrective action as soon as I can.
This letter of apology was the first thing I made upon learning of the mistake. I have already talked with the sales clerk concerned and he assured me that it was not intentional. He got confused because of the large number of customers that day and he too would like to extend his apology to you.
Should you have the time, please feel free to visit our store so we can resolve the matter in a way that is advantageous for both of us.
Thank you very much and I hope you can accept our apologies.