Idk why but I got perma banned for no reason..

So I was just playing a game, minding my own business, until I tell this Rengar that he got our turret destroyed. Not toxic or anything, right? He doesn't saying anything, and then I say "Rengar, you gave them first turret". I did get a little mad, but didn't flame. Then, him, Renekton, and somewhat Azir gang up on me. Rengar starts calling me out when I die, and then says "youre such a c**ksucking idiot hop the f*ck off the game youre a joke" (the exact words). I tell him to stfu cause I was just mad at the time. That was one of the only things I said that were toxic. At the end game screen, I tell the enemy team the exact words he said. He then says "i didnt say that youre crazy lol". They believed him and they reported me. I then get perma banned. I was toxic in the past but I wasn't trying to be toxic anymore..