It seems like Riot went through a ban wave for intentional feeders, because your recent caitlyn match seems pretty suspicious (along with two other recent players on the boards showing similar signs on their match history). Buying tear for champions that don't typically build anything from it along with a horrible kda seems to throw up a red flag for intentional feeding (since it usually is).
But given your level, I'll just keep it to a healthy scepticism and admit that it's possible you just like using manamune on most adc's and you played horrible that round because it was just a bad game.
If you weren't intentionally feeding, I would recommend you check with support to confirm if that was the reason and then argue your case against it if it was.