STILL LOSING RANKS AFTER WINNING GAMES

Over the past 50 games of Team Doubles, my brother and I have won 45 games and lost 5. I’ve only ranked up from a 14 to an 18.Every time the enemy team quits out in the middle of a game, it apparently counts against our ranking and delevels us. It’s gotten to the point where we let the other team kill us in order to keep the game close if necessary (so that they don’t quit out).What can we do to fix this?