A complaint letter should contain your details, a brief description of what happened, the reasons for the complaint and your suggestions and/or requests to solve the problem. Insert a reasonable deadline for response. Ten business days may be a reasonable timeframe.
Prior to drafting a complaint letter, gather all supporting documents, such as sales receipts, warranties, contracts and work orders from the purchase. A detailed and well-motivated letter will attract the attention of the recipient; a complete description of what happened will facilitate the internal assessment process and speed up the resolution.
Send the letter to the seller. You may be able to solve the problem by addressing the letter to the customer service representative, but try to include also supervisors and managers as addressees. That gives the letter more relevance and can help if you eventually need to escalate with further letters.
If you do not receive any reply, file a complaint with your local consumer protection offices, the Better Business Bureau or the state regulatory agency that has jurisdiction over the seller. If you have been the victim of a fraud, you can contact an appropriate federal agency. Finally, if none of the above options works, you can seek legal help.