A letter of complaint is a letter in which you describe a specific problem you have with something a company does. If you pretend The Truman Show is real, you might join the “Free Truman” campaign. You could write a letter describing how you think it is wrong to keep a human being in an artificial world, where his parents and friends are actors. This could be described as cruel, and could lead to severe psychological trauma.
You will want to include your specific complaints about the show, your specific suggestions, and contact information. I have attached a form provided by the government.