Can you help me get out of this?

I don't know how to win in this game.

No matter what I try - I tend to end up losing as of late.

I'm Diamond 5, but my MMR has descended to such badness that I'm being matched with Plat 2s and Plat 3s.

No matter how well I do early game - there's usually some factor like a ragequitter, person who refuses to group (like a Riven that only went in 1v3 and 1v5), or other thing out of my control that throws the game.

In other circumstances, I just don't win lane, or I just tilt because I start getting shit talked and people tell me to afk after 1 death.

Am I playing the wrong champions? I've been playing Zed mid and wanted to try Katarina and Twisted Fate or Ezreal adc.

I need to know what champions to play in what role so I can win games http://na.op.gg/summoner/userName=m5%20lessthanthree

I need the easiest, cheesiest, most OP nonsense that fits into mid, jungle, or toplane.

Honestly I've gotten to point where I've surrendered at 20 so many games in a row where the scoreboard is 5-18 or something that I have no spirit to fight anymore.

I was also a top rated Viktor main last season and am still this season but the tank meta hurt me so bad. Tanks were on me 24/7 and if they weren't on me lategame they sure were in my lane first and there to stay