Your gamerscore has been reset and you have been labelled as a Cheater for everyone to see, because you have modified your gamerscore.
As a result of this, you will not be able to earn back any achievements you had before, you will only be able to unlock achievements on enw games that you play from now on. SO you can't "fix" it really.
If you want an official answer, you will need to post in section 14.
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