When you know you're better than your rating but you keep blundering

Given that I have spoken openly about own blundering issues, I am not in a position of giving advice. But, I do sympathize a lot with your situation.

I'm finding that focusing more intently on the other player' plans and next moves has helped me so far in my last few games. That, and analysing my game and noting in upper case my blunders, and then chess tactics in a category that I know needs improvement or that I feel my board vision needs work on, for an hour or two. 

I will just say this, though, from personal experience, that even if you have the knowledge but still blunder when you play, you will lose. Chess is merciless, what counts is what is on the board. You may build the most magnificient car in your garage, it remains a lemon if the engine stalls randomly at traffic stops.