Campaign not working

Me and my friend did an all nighter playing the campaign on Halo Reach all last night and didnt recieve the CQB helmet… I looked why and it said i did not recieve the completion of 2 mission Achievments which are… EXODUS and ONI: SWORD BASE. I completed them again 2 times but still it didnt do anything… PLEASE fix it I would ever so much love the helmet and tell people i beat the campaign on LEGENDARY. Thanks.

Go into Halo Waypoint on your 360 to unlock it.