I got doxxed by a troll on a forum , the troll posted my real full name and school including my grade level , pics of a Facebook account which the troll thinks it's me but isn't because I don't have any mainstream socials. The troll keeps pasting my name and pics from the Facebook profile everywhere on the forum, what do I do ???
Delete all data from the previous account and make a new one. Report the troll to moderators. Consider never visiting that place again if the mods won't help you with the harassment.
If the troll doesn't have access to the forum's server, then all you have to do is learn some opsec and be aware of what you share with strangers on the Internet.
If the troll does have access to the server and you absolutely need to visit the forum (which I'd advise not to in such a case), then in addition to what has been said above, use VPN with a hardened browser or Tor to access the forum.
Shit I ain't a saint, we all can better about it. My point is that if you wanna go in the offensive online, be sure it can't bite you in the ass, at least in this regard.
Doxing is legally classified as harassment and is a criminal matter; contact law enforcement. Even if they don't do anything you'll get in their records so when your harasser tries to do something (like swatting) they'll know that something is up.