I highly doubt anyone was cheating in bronze/silver, but the way to deal with teammates doing poorly is to just not worry about them. Yes you are going to lose some games that you played well in because your teammates did bad but that is just something you have to deal with. Treat every game as a learning experience and try to figure out what YOU could have done better that could have possibly changed the outcome. Sometimes there really won't be anything you could have done but a majority of the time there are instances where you could have done or not done something that would have been a larger benefit to the team.
With this mentality you will improve your play and climb without realizing it, so don't focus on the wins and losses. Also try not to tilt, some times you just go on a losing streak, it happens, but don't get all bent out of shape about it. I had won like 4 out of my last 20 last week and in the last couple of days I have won like 9 out of 10 so just play to improve and don't worry about the outcome.