I got banned for cheating but i didnt even cheat like what is this i even appealed but rejected it

It is possible to get 0 inaccuracies, 0 mistakes and 0 blunders even without cheating.

Moderators have more data than us on what actually happened. Even I have a game with 1 inaccuracy and no mistakes or blunders beating stockfish level 5 in unlimited time without using any external assistance. That one was 22 ACPL.

In this case it is possible that the user actually cheated.

#21 possible yes. It is possible.
But why? A lot of the moves seems like straight forward counter moves for someone on his level.
But as yourself stated, we don't know.
I saw no indication of cheating in that game.
So, it's also possible that it's an error.

Personally I always give the player's the benefits of the doubt.
Even when I find something suspicious, I report it with a big question mark.
I don't know what evidence Lichess has.
None of us do. So morally, I believe people are innocent until proven guilty.

I have seen people successfully make an appeal.
But under what circumstances they did so, I don't know.
Let Lichess be the judge in these matters.

When your appeal is denied, means a team of moderator have reviewed your case and took the decision. There's no point of analysing your games on a public thread. Lichess has robust method to take decision on each individual case.