There are no brackets to "get out of", player rating is a continuous scale (I mentioned brackets to keep it simple, but it's a concept that is only used to categorize replays).
Increasing your rating is not just winning games, it's also improving in general; the MMR takes other variables into account, like your performance, the amount of games you played and more.
If you really think it's not your fault, then ditching AP might be a good start. Try playing some SD/RD/AR if solo queuing, or CM if playing with friends.
Or just forget what I said and find a pub stomping 5 man stack (might be harder now that they introduced Solo mode).