First, you don't get banned just because of a high number of reports. Reports trigger a review of your account, and if nothing punishable is found, then you won't be punished. If something punishable IS found, though, then you will be punished.
Second, a few months ago, Riot implemented a new escalation punishment system for chat related punishments:
1 - 10 game chat restriction
2 - 25 game chat restriction
3 - 14 day ban
4 - permanent ban
With this escalation system, once you reach one tier of punishment, then your next offense will always push you up to the next tier, no matter how minor the offense is. In cases of extreme offenses, Riot will skip escalate the punishment straight to a 14 day or permanent ban. sipping the chat restriction punishment entirely. Of course, if you go long enough with out being punished, then you can drop to the next lowest tier.
With your case in particular, I'm going to guess that you had a 14 day ban somewhat recently. This is essentially the final warning as it is the last step before a permanent ban, and you decided to ignore it and continued behaving in a negative and toxic manner. This lead Riot to permanently ban your account, as they believe that you do not wish to reform your behavior, and by doing this they are basically asking you to take your time and money elsewhere as they do not want you to play their game. Now, without seeing your full chat logs, I can't exactly say if this is the case, which brings me to my third point.
If you want people to believe you in that you shouldn't have been punished, you're going to need to post your FULL chat logs for us to see. From there, we can decide whether or not they were worthy of a punishment.
