Alright, let's try Buggie's UserMute mutator. Here is the release page for more info:
https://ut99.org/viewtopic.php?p=128337

I've installed it on the London Combo server. If you open console or use tab for quick console you can then type mutate mute and it should open the following window where you can highlight a player name and click the Mute button if you no longer want to receive chat from that player. You could also make a keybind for the mutate mute command if you find yourself using it a lot.