Trolling goes unpunished

Ok so I've gone into a ranked game, and one of my teammates picks Janna as jungler. My mistake was that I didn't dodge, but my problem is with the actual player. He even admitted to be trolling, and after someone pointed out his last 15 games were lost, he said "i trolled 15 whole games". How can he troll for 15 games and go unpunished? Is the report system that bad? I mean yeah, I get it, you can go trolling a few games before action is taken, but 15??? That's a bit much in my opinion. This has ruined the game for me, to know that you can go doing whatever you want, make the experience bad for other players without any consequences. And I'm sure this isn't the only case. I've attached the one screenshot I took below, and I hope Riot is going to do something about it, because at the moment, it seems to me like they don't care that much. Maybe I'm wrong, but that's how I see it. [Screenshot of the chat]( Have a good day. Edit: Updated the image (usernames no longer visible) and a few spelling errors.
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