I just beat Halo 4 on campaign on Legendary Solo. I did not receive my Master Chief Armor for match making. When i look through the Campaign Mission list, it shows the Legendary symbol on the Solo spot on all missions.
check waypoint. see if it says u finished all the missions. coz, iff u played offline it wont say u played it.
i hope u know what i mean, english is not my first language.
The first two missions are missing in your service record. Do them again and make sure you are playing while you are connected with XBL and get the commendations for completing them 
Is it only the first two? How do you check?
Commendations are how you unlock additional armor and visors in the game.
If it bugged out and didn’t complete it you have to replay it, solo or co-op.
Start(Spartan Hub)> Up one tab> Commendations> Player> Campaign.
> Is it only the first two? How do you check?
It says here: https://app.halowaypoint.com/en-us/Halo4/XxxTrisonxxX/campaign/
At my service record mission 7 is missing, but I do have the armor… Now thats weird 
right after completing that mission I got the message that I completed it and got the commendation, 1 minute after that my Internet Service Provider decided to do some mandetory maintenance, so my Live connection dropped out.
In short: make sure the commendations are received in-game, the website is not entirely accurate… but it’s a start