How to stop hacker?

Press ESC, leave game and search for another game. They won't stop.

Hackers stop you. But in all seriousness I would advise to just report them.

report them, otherwise you will have to surpass them in knowledge so you can either hack them or atleast kick them out of the server

Reporting them is the best option. Or contacting a support

You hack them back

No just kidding the only things you can do is report them or stop playing.