You can't do anything.
Sure, there are theoretical avenues for you to pursue,
if you have genuine, reliable, admissible evidence,
and you can persuade somebody
in the relevant jurisdiction to take an interest
in what seems to be nothing but a gamers' tiff.
But none of those avenues are all that practical,
are certainly not cost effective,
and may not even be enforceable.
It's a game. It's a
game.
Give it a rest and find something to do in the real world
(as old-timer net heads say, in "meatspace")