Avatar reward problem

The other day i got the achievement “Knight in White Assassination” and did not receive the avatar award that comes with it. My brother and my girlfriend got the same achievement in the same spartan ops mission that i did and they both got the knight helmet for their avatar yet i did not. I called xbox live to see if they could resolve the issue and after 30 minutes of trying different things they couldn’t fix it and they sent me here.

Has anyone else had the same problem or know how to fix it? It’s not really that huge of a deal since i probably wont use it anyways, but i paid for the game so i’d like to have the option to use an item that i should have unlocked