I play the games through to the end and play Fair and clean, i dont use a mic and When the players line up claiming victory or defeat it brings me to the main menu and tells me Im banned. I rarely leave a game and This happens frequently. I have only intentionally left four times.
Sometimes bans take a little while to actually take effect and in your case, it took effect after one of your games ended.
What does your ban message say, if you don’t mind saying? It should give us some insight on the reasoning.
Also, please check this Halo 5 ban FAQ topic.