I'm starting to get annoyed with the banning system

I just played an ARAM game and Riven (I'm not 100% sure it was riven but I will just assume it was) wanted to trade with Sona, however Sona did not accept the trade. Apparently Riven bargained to give a skin boost for the trade but Sona didn't accept the trade whilst not saying anything (she's Sona). As a result, this triggered Riven to announce that she was going to intentionally feed and two others (who I am 99% sure were her premade) announced in chat SEVERAL TIMES that they were going to intentionally feed.

And in the game they did just that. To be fair they didn't just run in, they were rushing in and using their abilities, however it was clearly intentional feeding as they just stood in the middle of their team and would dive through 5 of them (including towerdiving). They also continuously talked in all chat about how they were intentionally feeding.

At the end of the game I reported all three of them for intentionally feeding, and to my suprise over an hour later I got no notification that they were punished. I have no idea how they didn't since they constantly were giving evidence in the chat that they were intentionally feeding, but they didn't. Riot please [zombie-nunu-bummed]