A letter practice about complaint

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Dear sir

I am writting to you regarding some problems we have experienced recently with our order and to ask you to remedy the situation. I would be grateful if you can help.

First of all, you have provided us the wrong orders for three times in each of the last two weeks. we asked for 10 reams of A4 paper, but what you sent to us was A3 paper. It has resulted in delay of our work to print our documents that needed to present to our customers.

Secondly, you are unable to deliver the things on time we asked, such as pens, notebooks. Our orders often delayed for two days in the month. Your operator just told us that you would do you best to meet our needs when we phone your call center. It has significantly reduced our work productivity.

We have been working with you for the last five years and have always been happy with the efficency of your services. However, you will appreciate that we can't allow the situation to continue. Othewise, we will have to look for another reliable suppliers.

If you have any question about the problems I have raised, please do no hesitate to contact me. We are looking forward to your prompt reply.

Your sincerely

Frank