Alright... I'm gonna offer my two cents here and you can do with it as you please.
I used to do exactly what you did up there in those screenshots, which was to provoke them to say more so I could report them for more stuff and even share screenshots of their poor behavior with Riot support.
Dude, sh*t ain't worth it.
As soon as someone says something that is reportable, mute them. Don't tell them what they did wrong, don't tell them they're getting muted, don't tell them you're reporting them. All of these things can be considered toxic and unsportsmanlike, and if you get reported then something can be done against you.
The way the Instant Feedback System works is that it only takes ONE report to flag the match for review. This is why it is better to just mute and report without being toxic yourself, and save yourself the headache of having to do deal with people like this. You will also protect yourself from being "counter-reported" and ending up punished yourself, which is likely what happened here. It's no excuse that they did it first or what they did was worse. It's an automated system, and if it sees something wrong with your behavior then you run the risk of being punished as well.
tl;dr just mute and report, nothing else.
