Dear Ms Jeremy,
Thank you for your letter of 6 October. After supplying your restaurants for 5 years, I was extremely sorry to hear that the batch of bowls and forks which you received on 2 September was not of usual quality.
After careful investigation, we found that the cause of the problem was a faulty packing machine. It has now been repaired. I can promise you that this type of problem will not happen again.
According to the sales contract between us, we will, of course, replace your faulty delivery free of charge.
I would like to offer our apologies once again and thank you being an excellent customer.
Yours sincerely，(Your Name)