I called them in March that I want to do change of ownership and their agent told me it’s not possible

I called them in March that I want to do change of ownership and their agent told me it’s not possible. It’s a 2 year contract and I need to honour it or else they’ll blacklist me. I then informed her to go ahead and blacklist me. They harassing me with calls now about instalments that is not paid whereas I don’t even own that vehicle.