I've been permanently banned for third party software even though i haven't used it.

I got home to play some lol but as i was trying to log onto the client i was denied access to it and was told i have been permanently banned for the use of third party software. I'd like to know how this happened and if i can have it reversed as i have no knowledge of using anything like this in my life.

I'd appreciate it if I could get some help on this, as i would like my account back. (obviously)

Also every time i click the client it goes straight to the message for the ban, so i currently can't log into another account even. So basically i'm unable to play any league of legends