still debitting a cancelled contract

On January 6th my vodacom contract was cancelled on a premature basis and was settled with the quotation given by a vodacom representative. On Jan 25 2016 another amount was debited by Vodacom on my account so I phoned the accounts apartment and asked what was going on? The representative told me that Vodacom only gave me a quotation and that I am still liable for an invoice which was not calculated into this quotation. NOW VODACOM I ASK YOU, WHAT IS THE POINT OF ASKING FOR A FULL SETTLEMENT AMOUNT OF A CONTRACT if I still need to pay for an invoice which was not calculated into my original request of a cancellations quotation which I was not aware of which would be the case. This contract number has been set over to prepaid and I got confirmation that my contact has now been settled and cancelled. surely you have been doing this for a long time and should have fixed this, is this in contravention of the CPA<br> please refund me and stop debitting my account