The only thing you can do is mute these players and try to keep it a positive experience go about your game, don't talk toxic stuff back but only say nice things, don't even threaten reports.
The reason is because these days every time someone does badly for (X) reason a player always generally starts harassing chat accusing a person of Intentionally feeding, I have as a player went through this over and over again, and I am not just talking about League OF Legends, where currently I am banned from playing because they think I feed Intentionally, but other games DOTA 2, Smite I can do just as bad, and never been banned from them.
While I agree that compared to League I suck at DOTA, you know what happens when I play with someone else I generally feed most of the time, or do a lot worse than I normally would, when I play solo I generally do a lot better, I think my problem is generally playing with most people who don't play similiar type of play.
Playing a Bot Role for some players is harder than it is for others, and yes players do bad, the enemy gets two kills, do you even understand who has the advantage now (The Enemy) If you go into a direct (All in fight) who is likely to win (The Enemy) not you the except being certain champions, and quick plays, for example all in Annie Support combo + Immediate ADC follow up you can do better. ( In General with a skilled bot lane player we can easily kill an ADC in under 3 seconds, regardless of the support being played on enemy team most of the time.)
In general being a player for years, I remember League OF Legends before all this toxicity suddenly started happening, and the game used to be great I remember when people wouldn't get mad for going
Mid, or
Top, Does anyone here not played as long as I have to Remember the old season when Sivir was one of the most over powered champions in the entire game?