Im not getting credit for legendary missions

Ive been doing the halo campaigns on legendary to eventualy get the “Legend” achievement. Ive completed Halo 4 on legendary already but havent got an achievement for doing so. I am also missing achievements for finishing specific missions on both Halo 2 and 4. Even though it says i completed them on the game its self. If anyone could help me out with this it would be great cause i put alot of time into this and rather not repeat these missions.