This is a really troubling question. I'm a Nigerian and a student of the university of Port Harcourt. My school is like a cultism hub so unlike most of the people here, I have a very good idea of how horrible it can be. Cultists are basically the bullies of universities. For those that haven't had any experience with them, imagine high school bullies that are armed with guns and knives and regularly get high on weed, drugs, alcohol. That's a cultist. They are dangerous and I can't understand why anyone would want to be one of them.
Now as a parent I would be even more appalled at the thought of my offspring being part of such nonsense. I wouldn't even know where to start with the issue. The painful part is that a parent might even blame himself for it. They might begin to feel that they didn't raise their child well enough or they didn't do something right in the child's upbringing. But either way I'd have to face the problem and solve it.
So I'd call my kid and talk to him. Hear what he has to say because that's the kind of guy I am. I always listen to what people have to say. There is no excuse for being a cultist but at least he'll have a reason for it. And I want to hear it.
Now this is where it gets tough. Cultists like to believe that no one can talk to them. Like all bullies they feel they are the "top dogs" and are on top of the world. If he decides to ignore me or threaten me then that's where everything will pop. I'm a peaceful man but I hold discipline in high regard. Parents should discipline their children and I will. I'll beat the cultism out and hammer good behavior in. Then I'll withdraw him from whatever school he's in and send him elsewhere. No son of mine will be a social nuisance. No child of mine will be an oppressor. It is truly a painful thing to feel that you've failed as a parent but it is worse to give up