People that want to learn to play better in any sense will try to play whatever class they pick to the best of their abilities.
You know what people don't do? Join a class, go melee-only and be obnoxious by spamming every single form of communication (in-game chat, mumble chat, and lobby chat) with nonsense and in general acting like a troll.
If you want to improve while working up to the 25 lobby requirement to play medic, play classes you are also decent at and actually try to do good as them, that way when you somehow finally hit 25 lobbies you won't be caught with endless hate from all the players you caused grief to when you try to play your actual main.
The ban stays, read our rules, look up some guides, do whatever you need to adjust yourself in such a way that you aren't going to be causing trouble with this community.