So I was assigned mid, but the support took an ap champ and just went mid anyway. so I was mid and he was mid. He continued to take every cs and refused to support. If this happens, is the only way to avoid getting punished to go support? Pretty bad system if you ask me. If you get mid, you shouldn't have to go to support cuz of 1 toxic player just to appease your teammates.
You are totally fine to go mid and attempt to CS as well, and to report him if you want. I can't honestly say I know Riot's policy on this, but to me it sounds like he's not aiming to legitimately play off-meta, but rather to strong-arm his way into a specific position, which I'd say is a reportable offense. You playing your assigned role should not get you punished.
Did you actually receive a punishment that you would like to discuss? By the tone of your post its a little unclear.
Sounds like a normal game. If it was, there is no role assigned.
IIRC, draft roles are enforced with bans if your team does not consent. But this requires manual review aka front page of Reddit.
