Here's a sample to help you write a complaint letter about a product or service. Consumer Action offers a sample complaint letter and an email complaint template.You can cut and paste these documents below. First of all, you should write your complaint in details, and in good language. To Whom It May Concern: I am writing today to complain of the poor service I received from your company on June 12, 2020. Find out how to craft a formal complaint letter. Learn about key components, structure, and tips for an effective complaint. Be clear and concise. Describe the item or service you bought and the problem. Draft your letter on both e mail and your word processing program.