My account got banned but it wasn't me who got it banned?

My old account Kindred suprise got banned somewhere last year. Some guy logged onto my account I have completely no idea how he found out my password and username. Then he went on a game and just ran it down mid being super toxic. While all this was happening I was in bed. I told Riot it wasn't me but they said they checked thoroughly 2 times?

It just feels really unfair to have your account banned unfairly. I haven't shared accounts with anyone. Riot banning that account really makes me sad invested a lot and made a lot of memory's on it.

I am just hoping if someone logs onto your account with a different address riot will notify you

Also if you look at the match history something is obviously wrong https://gyazo.com/a19e216a2824bb46e3906e45f75329d2