It is a fairly simple task. Start with who you are addressing it to,"Dear, ...." (also try not to use,"to whom it may concern." know who you are complaining to) Then like any other letter you skip a line or two and indent. Then you could start off with something like,"It has came to my attention that...." Just be sure to be nice but firm with your words. Then at the end say something like,"Thank you for taking time to address this issue, Here is my email,
[email protected] (or/and your number) if you would like to get in touch with me."
Sincerely,
Clark.