1234, Main Street
Boston, MA 02123
<Recipient Address Goes Here>
I ordered a [Product/service name] on [date]. But, I was dealt with extremely poor service, and I decided to write and inform you about the same.
I may continue being a customer of [Company name], but that can be only possible when this problem is solved out.
Please contact me and inform me that what you can do about this, even if the possible solution comes out to be simply [Solution].
Thank you for your attention to this matter.
encl: <List of enclosed items goes here>