Being charged for something not used

To who cares I got confirmation that my MTN contract was Cancelled round about 5 months ago only to have their attorneys contact me and tell me I owe MTN money now I do not understand how that works since when you cancel a contract it gets cancelled and payments stop. So I went in to a MTN store only to find out that my sim has been cancelled and not my contract where I asked them to cancel both since I want nothing from them again. Now I am wondering how competent the people are since now I owe money for something I stopped using about 6 months ago and was supposedly cancelled. So please tell me what is going on since you cant be helped by any of your stores they cant give you any information or cancel anything and calling one of the numbers takes forever to get through and then still no help. And I would like to have a detailed list of the payments on what I apparently owe and used during the time that the sim was cancelled and I stopped using it.