I was banned in April but haven’t played since December. Help?

My account was banned on April 21st 2018 and I have absolutely no clue why. I didn’t even know anything had happened until I tried to log in today. I’ve never had any suspensions, warnings...nothing! The closest I’ve gotten to ever getting in trouble was being reported by another player for my bad connectivity (which I totally understand, I’ve learned to never play PvP without stable internet...it was a rookie mistake) I’m just very confused. The last time I played League was in December of 2017, it was just one or two games. No swearing, screaming, or otherwise foul/toxic behavior. To be honest I rarely even use the chat because I’m often on a team with my friends who are in the same room. So I’m confident the ban is not behavior related. The email says I violated the Terms of Use but doesn’t give me any more information. I can’t figure out why I’d get banned 4 months after the last time I played and seemingly over nothing. If anyone could help me out in understanding what I might’ve done or how to solve this I would greatly appreciate it. I’ve submitted a support ticket but I’d like to get the communities opinion so I can make sure nothing like this happens again.