Well, how we fixed this back in time..
we bought a Double XP from the Prestige Shop.
(Mostly like for they who didn't have it from before and just hacked to get it, and that would be the problem. how to remove somthing you really don't have....)
And then we sat the value to 0. /(As mention in 2 or more posts above.)
Then you play a round and it should be fixed.
Also, this isn't really hacking.
Because you regret your actions and want to remove it.
And it don't ruin the game for others.
That is mostly like why Stat editors haven't been bannable for a time.