Please explain your complaint: Try to be brief, but be sure to tell WHAT happened, WHEN it happened and WHERE it happened. Here's a sample to help you write a complaint letter about a product or service.The more information you provide, the better we can help you. 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 file a complaint, fill out the electronic form below. Take a look at this example complaint letter for ideas on how you should approach writing a letter of complaint. Be clear and concise. Describe the item or service you bought and the problem.