Vodacom Charging for Canceled Contract

I canceled my contract with vodacom last year December. For the past 3 months I have been getting an account from them that I owe them for data. When I called in January I was told not to worry it definitely canceled that charge was for data I used out of contract. But February and March I no longer had the sim in my phone so I know for a fact I did not use it for data. I called again yesterday and I was told to call another number to find out why I was not canceled. Vodacom is steeling from us.