I'm lucky, I guess. I've not had to deal with trolls too much.
Not on-line anyway.
In real life, I have known more than a few poopyhead meanie-faces. And I knew a fella who said, when such folks started stirring shit up, "Cut 'em out of your life like the cancer that they are."
It isn't easy to do, especially if those toxic people are supposed to be friends, or--worse--if they are family. If someone is constantly a source of contention or of negative emotions, its time to evaluate the pros and cons of severing ties. If they are growing on you, sucking up your resources and giving nothing back but dis-ease...cut 'em out of your life. (Again, I know that in cases where the person is family this is sooo much easier said than done. And in cases of family, it is surely worth trying other avenues first. Such as learning how to spot their tactics and diffusing them. A good counsellor is worth your time in such situations.) That blocking feature on Facebook and on phones exists because, as KAK so delicately put it...Assholes happen. Listening to these people gives them power--the consideration of your mind. Don't give them that. Don't even read a text or an email. Email marked as spam never sees the light of your inbox and you aren't tempted.
I've done this. It isn't easy. They try to worm their way back in. You want to give them the benefit of the doubt because, well, you're nice. And they know that. 'Nice' makes for an easy target. But don't stop being nice and being you, because that would in a way let them win. Just educate yourself, as in learn to recognize the tactics of toxic and manipulative people, and put up the buffers.
Then live your life...happily. It's the best revenge anyway. :)
A couple of links: