How on Earth do you END non-aggression pacts?

I just want to exterminate my neighbor. His influence is taking over my entire empire and he's about a third my size and lowest in all rankings, I literally have culture starbases every 3 tiles in a ring around the guy and he's still coming! I can't attack him, I can't declare war on him. All we have is a non-aggression pact and there is no way to end it, it is literally nowhere in the diplomacy screen it's not in "let's discuss something else", it's not in "trade". This has to be a bug surely? I've seen other threads say it's literally a clickable option in diplomacy yet it isn't. It literally isn't, it isn't anywhere in diplomacy, at all.