Like Pyrosan said, you'll want to file a Support Ticket, but before you do that, I want you to at least look at your match history. You play often enough, but you had a short break, and afterwards had four matches, three of which look suspicious.
And, when I say suspicious, I'm not implicating you of having used 3PS yourself- more, it's probable that someone broke into your account and did so. I'm no expert, but your general performance seems pretty modest-to-poor up until that Xayah game, and the only match you had that came close to that sort of slaughter was a Lucian match a while ago - but you didn't go so far unchecked as to have three deaths then.
Add the Sylas matches to the mix (It doesn't look like you've played Sylas 'til that day), and I think it's likely that someone hacked your account and ran third-party software while playing it.
So, when you file your Support Ticket, you may want to ask if Riot noticed any atypical behavior on your account, and whether or not it may have been compromised, and if so, whether or not you could get it back.
Best of luck on your Support Ticket, and if you need any more information, I'd be glad to provide what I know.