Simply put you won't win every game even if you are the best player. Even the best players in the world may have 54-65% wins. The point is if you win the games you should win, and win 1-2 that you shouldn't win... then you gain ELO. Think of it more like baseball you got to play lots of games to see where your skill level really is.
Also you blame your allies for trolling. Remember enemy teams troll too. Statistically if you don't troll your chances of this happening to you are 20% less than the enemy team. So if you are better than your ELO, then you'll win those extra 20% of your games and start climbing. If you blame your allies for your win/loss instead of looking at your own play you'll never move up. Lets take my ranked match game history:
Nunu: 5/3/20 summary of game: Most lanes were neutral, but I managed to help our adc get 22 kills in 24 mins. Obviously we won as a result of this in quick order. Allies trolled in champ select fighting over top... yes I won with trolls on my team! *gasp* I simply requested in pre-game that we save hate for each other until after the game and amazingly they agreed. We worked together and secured bot lane so fast it wasn't funny.
Ashe last game I was 16/4/12 Summary of game: Had a blitz on our team who trolled. Was supposed to swap with our garen and go top but didn't. So our Garen had support masteries on top and was cussing him out. Once again I requested we save it for after game and just try our best because I have won with worse things happening to me. Garen agreed. Blitz actually didn't play great but as we all know lux fails as support against ashe and blitz only had to grab once or twice before I completely locked up bot lane for a win. Then we pushed objectives in all other lanes and I kept collecting kills. So I won game 2 with trolls too.
Ashe 13/9/12 defeated: I managed to win laning phase and took bottom turret... My support was a voli and was not overly great... Now I still won the lane and went roaming afterwards but they had a kat + jarvan and both were able to get on top of me because no one was peeling people off of me and I didn't get good openings to attack the enemy team. Simply put I had no protection trying to snipe enemy team and got owned. I could have done better at not falling for bait a couple times (even when they did net me kills). It was not entirely my team's fault I didn't carry them to a win of course I played a part too. No one trolled in this game and we LOST. That being said the reason is the enemy team just outplayed us in team fights. When you lose a game, it is sometimes because your team trolls, but most of the time it is because their team out plays yours. And being part of that team, a share of the mistakes were my fault.
Ashe again 11/1/8: This game enemy team had unusual bottom composition. I don't remember who they were supporting with but it wasn't a traditional combination. I believe it was vayne and xin. Anyways my support this game was pretty terrible, but luckily I was very good at poke harassing xin/vayne and my support would once in a while make a play to try and help. When they got a slow in I usually finished the deal. Once I got a couple kills and my ult I was able to lock down bot lane and go roam. Pushed other lanes and won in pretty quick order. Now of course my support wasn't so good and ended the game with dying quite a bit, but because I limited my mistakes I was able to carry to victory. My team was not overly good and other lanes were very neutral in KDA and top lane was losing. But I was able to win faster than he lost top and thus pressure lanes to keep it going our way.
Kassadin defeated, Summary of game AP yi simply could not be stopped. His range with alpha strike made it so I had to null him after it ended. I would win these trades but he would keep doing it until low then meditate... I would of course not gain health and he did. He simply pwned me because he could sustain alpha strike + meditate in lane the entire time and got CS high enough he could eventually dive me. I'm not sure how I could have played it worse but he went roaming and owned my team in general after I died a couple times. This loss was COMPLETELY my fault. Even now I'm not sure what I should've built instead of normal kass items. I need to do some study on how to play against him so it doesn't happen again or next time I will be just as bad off. Enemy team after game were saying they needed to report allies for trolling... so they won with trolls.
So just looking at my ranked games that happened in the last week you get the feel of how things are going. My placement matches have me around 1108 now. Because I'm still able to carry bad players I know that I will go up for at least a little while. maybe I get to 1200, or 1300, or more. Doesn't really matter but ELO reflects my ability to win the game REGARDLESS of my allies. I don't dodge games even where it looks like my team is going to kill each other pre-game.
Simply put your mistake is believing your teams are causing your downward slide. Remember this... no one EVER got better at a professional sport by thinking their team was losing them the game. Chess masters spend 4 hours a day for 7 years to achieve that rating on average. NFL players usually start training as tiny children and play their entire life. Any great person at any competitive event puts in time/effort into becoming as good as they can. You're still at the level you think your team is just somehow always worse than the opposing team. This mind set is your biggest limiting factor. You cannot think of games as trolls vs enemy team or your team is bad all the time. You have to think every game what you can do better. If you think you're so much better than enemy team you'll have more games like my carry games that I shared above than losses. If you have more losses, well then you are not the Tom Brady of LoL, sorry to burst your bubble. Great players make teams better around them. Learn from each game, download LoL replay! Study your own game see where you got baited. Look at every death and see how you could have changed things. Check to see if you had wards up the whole time. Find something you can fix EVERY game. That is how the professionals do it.