I heard that the challenge is bugged, and that you can't link your account if you created it recently, and that the staff changes the challenge if it appears, so, there it is, I didn't find anyone else giving the heads up so far.
If the bug was already fixed, how can I link up with my gamertag? When I go into my profile, it still displays my old gamertag, is there any way to change it? I already changed the e-mail and everything.