You can address negative or bad experiences to your employer or companies through letters. Download and use these complaint letter templates . Want to lodge a complaint in writing but have no idea how to do that? Well, don’t worry because here in this article, we have 12+ formal complaint letter samples and formats that can help you understand how to write a perfect formal complaint letter . A letter of complaint is a formal letter generally written to the concerned person or authority to address any wrongdoing, malfunction, or injustice over a product or service. This article on complaint letter format will provide you with tips on how to write a complaint letter and also give you a few complaint letter samples for your reference.