"Many people say elo hell doesn't exist, but I'm generally convinced there is... People get so bad in the low elo that they feed; not even intentionally, they're just horrible.."
If you're at 800 Elo, you belong to be there. I was around 1450 Elo in Season 2 after 80 games, and I climbed very quickly from 1250 when I started (45~ games for 1250-1450). If you're significantly better, you will win a large amount of your games.
So, the conclusion is - you're just as bad. Looking at your match history, I agree with that. First game, 2/6/2, 26 minutes, 58 CS. Second, 8/7/5 (alright score, but die less), 128 CS, 35 minutes. 9/9/4, 83 CS, 34 minutes. 4/6/4, 35 minutes, 89 CS. 3/2/4, 25 minutes, 86 CS. Etc. etc.
Look at my match history (ignore the proving grounds games - those aren't 5v5s and don't count):
8/2/2, 158 CS, 25 minutes. 10/9/5, 415 CS, 51 minutes. 7/5/1, 130 CS, 25 minutes. 4/10/12, 269 CS, 39 minutes. 38 minutes, 290 CS. 25 minutes, 190 CS. 36 minutes, 192 CS.
These scores are low by my own standards. I've been out of practice, and haven't been playing much lately. In general, you want 100 CS at 12 minutes, 200 CS at 20 minutes. Try for 10 CS/minute by the end of the game. You'll find yourself winning far more games if you have more items.