How does the ban thing work?

So ive been playing League of Legends for 3 years and played rank for like 2 and a half years. I've been playing over 1k games this year so you could say i have played with a lot off people. I have noticed that recently there have been a lot more trolls, inters and afk's than usual and I noticed the same last year that the longer into the season we get the more people seem to give up and rather start flaming inting or just leaving the games if they play bad. I know that if you go AFK a lot you will get timers then ban and eventually permaban but this week I have played with at least 5 players who me personally think should have been banned like a vayne who said she knew me from last year and that i have flamed her mother so now she were going to int she went predator and tp to follow me wherever i went. Like i have never met her or played with her my whole life still she is here ruining me and my teammate's games. she told us enemy adc were paying her to windtrade and harrasing his support for being an e-girl still. I cheked her match history and saw tons off games where she had gone the same and inted, and i can't understand how she still havent been banned. Im talking past 16 games she played vayne and was on average 0/10. Aren't they supposed to get banned for this? Meanwhile, I know people who said nothing more than ¨cait u suck¨and got a permanent ban. Like where are riots ban priorities. I know this was written a bit messy, but i hope you get the message. From a sad player :(