When writing a complaint letter, you want to keep it short and to the point to help ensure that your letter will be read in its entirety. If you write a seven page complaint letter, it's highly unlikely that someone will sit down and read all seven pages.The complaint letter should be addressed to the customer service/consumer affairs department or the head office if there is no customer service department. The address and contact information of the customer service department should be available on the company's products or website.