Submit a support ticket to Riot here: https://support.riotgames.com/hc/en-us
They take stuff like this pretty seriously, and you can rest assured that they will investigate the players who harassed you.
I'm sorry that people abused you that bad, it sucks. Just remember that they're just immature idiots who don't mean a word of what they're saying, they only say it because they think it will upset you. Not that that makes what they did any better, but for me it helps knowing that they don't actually mean it and that to them it's just a means to an end.
Also people who start acting toxic are usually going to keep acting that way. When the leona started ripping into you with verbal harassment you should have muted them so that you wouldn't have to read any more of it. Try and remember to do this in the future it can save you a lot of stress.
As for them reporting you, I wouldn't worry about it. False reports get thrown out, and the system is very good at identifying false reports.
Anyway I'm sorry you got harassed. You didn't deserve it. Good luck with your case, and have a wonderful rest of your weekend <3