This letter complains to a company that a purchased product does not perform as advertised.
1234, Main Street
Boston, MA 02123
<Recipient Address Goes Here>
<time you purchased the product> I purchased <product purchased> from your company. Since that time I have found that it <description>.
What I need from <company name> is a suggestion about what to do next, whether that means refunding my money, sending me a replacement, or referring me to another supplier. I look forward to hearing from you promptly. Thank you for your time.
encl: <List of enclosed items goes here>