My account was Permanently banned

Hello i had start playing league of legends since 4 season i was really fun of the game and try very hard to improve my skills into the game also i spend a lot of money into the game plus countless times of gaming and all was good until 2 days ago i try to log in into my account and a message appear saying that my account was Permanently suspended i was shocked, i look to my e-mail for further information and the message told me that i was suspended because i use 3rd party program the truth is that i used mklol before 5-6 months ago and riot send me e-mail and explain that this program is illegal so i delete it and never used anything again i had just download the game and play like a normal player without any 3rd party program i told them that was a mistake and i didn't used anything like that and i asked them that if there was any problem they could tell me to fix it and keep up but nothing happened and just like that without any reason i lost 2 years of my life and about 400 euros for nothing and u tell me that this if fair? from a large gaming company such as riot just banned account without even trying to fix the problem? Please someone help me with this cause its really unfair all this situation i just want to play the game like a normal player who spent 400 euros to this game.Please someone find me a solution to all this situation.