Verbally abused by a 4 man premade - how to report?

They said they are 4 man premade in champion select and asked me to give one of them mid, which I refused. After losing my lane, all of them flamed me and repeatedly asked the enemy team to 9x me, saying I was the one flaming them. What should I do in this case? Here's the link to a match in question http://matchhistory.euw.leagueoflegends.com/en/#match-details/EUW1/2559949259/22395521?tab=overview
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