Halo 4 award not being unlocked

I unlocked the achivement that unlocks the avatar award that says Platinum Mark VI Helmet Unlock the “Wake Up, John” achievement to earn this award.But the avatar item wasn’t credited to my account and it doesnt say that i unlocked the award on my dashborad but i unlocked the achivement “wake up,John” for the gamerscore.
what can i do to get the platinum mark VI helmet that i should have unlocked after i unlocked the achivement?