Achievements Hacked

Hello,

I was playing Black Ops 2 multiplayer (which as many may know is increasingly riddled with modders). Anyway, I joined a game which had a modder in it (which is annoying, but normally tolerable given that the effects are contained only within the instance
of the game match itself). However, in this case I suddenly started unlocking Xbox achievements for the game that I did not earn. I shut off my console immediately in the hopes that it would minimize the number of false achievements, but when I got back online
I still had 820 gamerscore worth of achievements that I did not earn added to my total.

Is there a way for this to be undone and fixed? I talked to Xbox support chat, and the technician directed me here. He said he believed a moderator would be able to look into my situation and make the necessary adjustments. Ideally, I'd like the achievements
that were falsely unlocked to be re-locked, and my gamerscore to be adjusted accordingly. If this is not possible, I'd appreciate just any solution that makes my gamerscore reflect reality again. My gamerscore is low enough that its only meaning to me is derived
from its total legitimacy which has been maintained until now. I'm saddened that such is no longer the case. I probably shouldn't care this much, but I've watched my gamerscore accumulate over the 7 years I've been playing on Xbox. So the number along with
the personal history it signifies is fairly sentimental to me; thus, so is its legitimacy. I'd appreciate whatever help possible. Thank you.

:)