I was permanently banned but all I've done was be inactive for 2 years? Need help.

I wanted to get back into LoL after a 2 year hiatus. I knew my account would have to be recovered because I got an email about a year ago saying if I didn't log in and play a game my account would freeze. I didn't play any games and just this week I tried to recover it. Player support just sent this

"The evidence we found on your account confirmed for us that the client played on was modified in a way to give an unfair advantage over others. We take the use of modifications very seriously and consider it an egregious act against the League of Legends community. The negative affect the account had on the community is irreversible and it had an extremely negative impact on the other players in the game. Since this is the case we will not be adjusting the permanent ban."

I am completely taken aback by this because I have never cheated and frankly wouldnt know how to do so if i wanted to. I've never used any other programs or anything. Anyone have the same problem before? Thanks.