Writing letters of complaint is a favorite exam task. Have you ever actually written a letter of complaint? What was the result?

I have written a letter of complaint to my broadband provider at home. The way the company handled my situation was very frustrating - misinformation from one department to another; transferring me from one department to another. I had to disconnect my line and switch to another provider as dealing with them was exhausting and wasting me a lot of personal time which I could use to spend with my loved ones.