Charges after contract has been confirmed to be cancelled

Previously complained about Vodacom, they contacted me and confirmed the issue is resolved, but here we are again. On the 4th January I settled with vodacom and converted my contract to prepaid. On the 21st January I received confirmation that I owe them R0.00 and that the conversion to prepaid would be active from the end of Jan. I confirmed multiple times with the agent that I OWE NO MONEY to Vodacom, and that the data they had allocated, they owed me. There was an amount reflecting as outstanding on my vodacom app, and the agent confirmed to me that my app was probably outdated - I owe NOTHING!... In March, I received a statement that I owe R150... I sent an email on the 9th January, and till today, the contact center cannot give me a clear response as to where this charge comes from. I am definitely going ahead to log a complaint through ICASA as your practices have become quite underhanded!