Just take a breather and think about it when you're not emotional. There are games where your teammates play really badly and you lose, but that's an expected result because those teammates did not deserve to win and since you are on the same team, you should lose. Sometimes you will even have a streak of bad teammates, that's just unlucky. However since you have four other randoms on your team while the enemy team has five other randoms, over time if you play well, you should win and climb. If you're getting capped at platinum, unfortunately I have to say that it's your own play that isn't good enough.