I think you’re french, but I’ll keep it in english 
Noone moderates Official servers. Only if there’s actual issues(eg. downtime) with the official server itself does staff have the ability to jump in.
See also: Is your server unavailable? Use our new report tool!.
However, if this is on an official server - your report concerns a player issue - you’re not able to report it.
Unofficial servers are moderated. If your server admin is on you can message them letting them know of the issue.
Friendly heads-up, reporting exploits -for both kinds of servers- should be done via the form, instead of a forum thread, see Found an Exploit? We'll pay you for it!
I hope this helps you, @raphael64.