Your Address Information:
Your Address
Your City, State, Zip Code
Your Phone Number
Your Email Address

Date

Salutation:
To whom it may concern:

First Paragraph:
The first paragraph of your letter should simply state the problem.  It should give as much detail about the issue as possible without rambling.  The reader of your letter should be easily able to understand your complaint.   While you may want to vent your emotions, it is best just stay concise.   

Middle Paragraph:
Use this paragraph to list all relevant information such as the product or service, people involved, addresses or location, dates, any serial numbers, model numbers, pricing, etc.

Next Paragraph:
Next, simply state what you would like them to do about the complaint.  It should be realistic but also specific.  Be sure to give them a time frame for when you expect them to right the wrong. 

Final Paragraph:
Lastly, thank them in advance for their help in resolving your complaint.  Mention any copies of paperwork that you may be attaching like receipt copies, any previous documentation, etc.

Complimentary Close:
Sincerely,

Signature:
Handwritten Signature
Typed Name