Poor service and turn around time

My contract was expiring in August. I gave notice to Vodacom to convert the number to prepaid. In September i received a bill to almost 3000 on the number i requested conversion. I contacted Vodacom on the first week of September to dispute the bill. The billing department referred me to data department since the query was about data usage. The data department could not assist since according to them no information is available on that number since it was converted to prepaid. They in turn referred me to customer care which i did not find any joy still. They also referred me to billing department. This vicious circle continued until i got tired without any joy in their service to resolve my dispute The next week also i attempted again and spoke to the lady in billing department and she promised to look into the matter. In the meantime she discontinued the debit order until the matter is resolved. In October the billing still not resolved. i contacted vodacom again and spoke to guy who promised me that the matter will be resolved in 72 hours. Nothing was done. The only thing i received are voice reminders about the outstanding bill which i find offensive and intimidating.