Witchcraft and its backfire

hi guys, I don't know about you but the place I come from has people practicing witchcraft. They sometimes go to the witch doctor to make somebody's life miserable. I hate all this and I don't believe in it. But I have this father in law who is suffering from the backfire of witchcraft. He locks himself inside the house and does not communicate with anyone except his wife. He is feeling that everyone is doing witchcraft on him while there is nobody who is doing that. he is always praying and reading bible but has no love for any of his children. Since I am new here, I don't know what there past is and why he is like this. but my mother in law said when the children were small they were very naughty and then somebody told them to see a witch doctor who can fix the problem. They thought somebody did black magic on the kids that is why they are giving trouble. Finally they went to the witch doctor and he told all the things that was true in their case and my father and mother in law were convinced that the witch doctor can solve there problem since he was correct on everything he told. I don't know what happened that now this fellow is suffering. I believe it is the backfire of the witchcraft they did in the earlier days that is why he is scared that someone is doing black magic on him. He is become a mental patient now. Now I know that black magic can be true and does exist. I have never experienced this in my life but when I see my father in law. I am convinced it exists. what do you say? do you believe in black magic? have you across any situation like this?