i don't know how to write an admin only if it's for the admin

You need to contact an admin on that server, maybe there are some connections, if not then there's no way.

In discord there is Danya 2.0 you write to him. As for cheaters there are none in Garry's mod if you mean that people join you or somewhere and break something then just fraps and post it on the forum and that's it but otherwise there are no cheaters