Ranked Flex; 3 men afk on base intentionally

Hi, So I played this ranked flex game and had a mid laner who fed and that's general, it happens at times, but to my surprise, him and his other 2 premades sat in the base calling 'open mid' for the rest of the game and said it is not a punishable act. They also claimed to 'know' all the tricks to not get banned by doing the same. I sent out a report for the same but received no acknowledgement like it is sent. The team surrendered at 20 minutes as the other solo flex person gave up to his misery as well. It is very unfair for players who are really trying to win a ranked matchup playing solo in a flex ladder. Is there any way I can send the screenshot for further evidence?
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