You do not get belt xp in quick matches. There is a bug going around where your belt won't appear on your badge in quick matches or where your belt might appear on another players badge. It's nothing to worry about. You badge/stats are still saved. Patch will be release soon.
I play Ranked matches. I don't play Quick Matches. It's still a problem. In Ranked my Belt doesn't display and after the match I'm getting no Belt XP. I play Raiden and get 1st/2nd place in almost all my matches. It's a glitch that needs to be addressed anyway
This might help a bit further if you answer this: Do you press X before everything is displayed (such as your EXP and belt points)