Multi's are ruining this game. Even if you don't think you have one in your league you're always left wondering.
I have a couple of solutions, if these ***holes are not going to get a ban, then I suggest dumping the league they are in, radical I know, but it really is no fun when someone is constantly trying to gain the upper hand unfairly. Also add in collusion between leagues eg: someone makes a favourable trade in one league to garner the same back in a different league.
The other idea I have is to offer an amnesty, come clean , contact JDB and say that you've made a mistake and get the account deactivated. All anonymously done.