Your ban was about your own behavior, not theirs. Punishment is dealt in escalating fashion in 4 tiers in order;
- 10 game chat restriction
- 25 game chat restriction
- 14 day account ban
- Permanent account ban
If you got a permanent ban then you probably recently got off a 14 day ban (looking at your match history, I assume that was a mere 12 days ago). Those temporary punishments are to give you time to reflect on and improve your behavior. In cases where a player continually refuses to follow the rules and disregards all temporary punishment, a permanent ban is the only other option. If you were to have changed your behavior then it would've stopped at the 14 day.
You are not simply given a permaban for severity of the offense, but the continuous lack of regard for regulations as well (any infraction, if done consistently enough, will eventually add up to a punishment). Are you unaware of this?
The other players' actions do not justify your own, and they will be dealt with by the same system which dealt with you. The mute function and language filter is not an accepted reason to be toxic, as by the time they are forced to use it the damage has typically already been done. Retaliation can only hurt the situation and does not make you not responsible for your actions.
As for them reporting as 4 people, it is irrelevant how many of them did; only 1 report is needed to get your match reviewed, and any more won't make the system check any harder.
When you get your reform card saying your case was reviewed within 20 minutes, that is the Instant Feedback System which handles reporting now (Rioter direct involvement is not common or always necessary). Punishment is dealt within 15 minutes of the final validated report.
https://support.riotgames.com/hc/en-us/articles/203066050-Tribunal-FAQ
https://support.riotgames.com/hc/en-us/articles/201752884-Reporting-a-Player
https://support.riotgames.com/hc/en-us/articles/201751874-Behavior-Worthy-of-a-Champion
Oh, and, could you share your reform card?
