I need advice helping a toxic friend
So I recently added a random account that added me, and in the voice chat, immediately realized it was someone I used to ranked years ago with. I had thought he quit league, because I never saw him on anymore, but it turns out he got banned typing something horrible. He was really bad about getting angry and screaming in voice chat, but he never used to type, and flame our allies. I stopped playing league ranked for a couple seasons, just finishing placements, and I think I'm kinda responsible for him raging in chat, because he couldn't complain to me about it, like usual. That being said though, he is even more toxic, and even when in voice chat, he will type in chat to take jabs at our jungler, which normally makes jungle ignore his lane while he feeds. I'm not sure if I should continue to help him, or cut ties with him completely, because he really does ruin the game for me sometimes. His highest rank was Plat, but he is hardcore losing/trolling stuck in silver 4, and is a support main. He abuses his adc every game in chat! I can't think of a way to help him, besides maby, sitting down on voice chat, and talking to him to see what's going on, and trying to delicately tell him he is being toxic, and ruining our games.
As an example, he made our jungler DC from a game in ranked, when he told him, he should have been swallowed..... Kayn had tried to gank bottom, and was 3 0 at the time, but had engaged on the enemies under tower right as Warwick was coming in for a gank. Leading to a triple kill, and horrendous flame. He helped me mid, camping, and winning my lane(I was a Zoe vs a Yas 1 trick!). My friend constantly harasses him, constantly telling him he needs to set up a tent bot, when they are pushing under enemy tower 24/7. Thanks for reading, and any advice will help.