Account compromised and then used third party programs...
I haven't played in a few months, but I just got an email saying I was banned for third-party programs. I just checked my match history and saw that someone played on my account for the past week with champions that would likely be used with scripts. Interesting.
If you check my match history all the way back from season 4 to season 8 I almost exclusively played Sona. Apparently this season I'm a Vel'Koz and Xerath main...
On the bright side, they got me placed Diamond again.
I assume support can verify that this wasn't me, but if not then oh well. I wasn't really planning on playing any time soon.