GIVE ANSWERS - English

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who can help me check my writen work. because i will take a exam for IELTS. please tell me if it was any problem.thanks.

Dear sir and madam,
I'm writing with regard to the fact that the other day, I bought a microwave oven costed
300RMB.Unfortunately, It was broke when i needed to heat the milk.During three months, what ever you bought any product have problem in my shop, it's allowed to change the new one.I have tried to contact you by phone but could't get anyone who knew anything about this matter. So it's very terrible therefore, you can imagine my mood when i discover it.
I would be greatful if you can return my money and offer an explaination for this poor quality of your servise.
Looking forward to your reply.
Yours truly.
carmon