вариант
Dear Sir,I am one of the permanent costumers of your shop. I bought a mixer from your shop last Monday. Coming home I decided to try the new equipment and I was so disappointed to find out it was out of order. I rang the shop up and complained about it. They told me it was their fault and promised me to replace it. I took them the mixer with the purchase check and they told me to give me an answer after talking to the shop manager. I left both my mobile and house telephone numbers but I have not got any answer from them till yet. Now I am writing you to complain about it. Please, arrange everything as soon as possible and either replace this mixer with a new one or return the money so that I can buy another one. It is my son's birthday five days later and I have promised him to bake his favorite cake for the party. I hope to hear from you soon. Thanks in advance.Yours faithfully,