Telkom not allowing me to go from contract to prepaid even though my contract is fully paid.

All I want to do is go from contract to prepaid. I have finished paying my contract/phone and would like to transfer to prepaid as I can not afford to pay anymore. I have gone into the store on numerous occasions. If it's not the system being down then the system is slow or the service is slow or the person helping me messes something up which blocks me from going to prepaid.. When I call the client centre and choose the cancellation option, no one answers. When I choose the billing option, someone answers immediately and when they transfer me to the cancellation department, no one answers. I have called numerous times.