Need help to find out what to do!!

I was playing leveling my other account. Take in mind this account is only level 13. So i did't know he was dc and so I killed him in lane. Once he came back I had killed him over and over. The game ended with a 20 min surrender. In the end game lobby he told me 3 times to go kill myself. This is very disheartening because if was a new to the game that would make me feel very bad and not want to play. I know there is not name shame but this was an unreal amount of toxicity. I have screen shots of this guy doing this in the post game chat. If i can get together to maybe IP ban this person for a short time I feel it would be one less extreme toxic player in the community. Please help!!

Sorry for bad English