'Domination' Achievement Glitched?

The Halo MCC matchmaking achievement 'Domination**’** will not unlock for me.

Earn a total of 100 Legendary medals in matchmade games.

  • I checked my service record in Halo MCC and I have the medals required to unlock both achievements. - I checked the achievement app on Xbox One and it said it still locked. - I’ve got countless extra SWAT medals and Legendary medals since I’ve hit the requirements still locked. - I’ve restarted my xbox, hard reset, deleted & recovered my profile - I have Xbox Live Gold - I live in the USA - I owe/play Halo MCC digitallyI’ve done everything I could think of short of trying to reinstall the game or factory resetting my Xbox One.
    This is my last Halo MCC matchmaking achievement**.**
    I have 15k gamerscore in Halo and I’m going for unlocking all the halo achievements again.

My life would be pretty much over if I came across a Halo achievement I couldn’t unlock.

What can I do to get my achievement unlocked?

I’m sorry to post again but does anyone have any idea?.. I can’t seem to get help anywhere, other forums, twitter, anywhere.
It’s disheartening putting so much time/effort in into Halo achievement hunting and have this happen… :frowning: