Incorrect Deductions

I have received my bill on 14 Jan 16 via email. I saw that the amount was incorrect and I took it up with Cell C call centre immediately. The call centre agent advised that they will phone me within 2 working days, on Tuesday 19 Jan 16 I phoned Cell C again asking for assistance, a gentleman phoned me on Wednesday 20 Jan, advising that another agent will phone me back with the correct amount BEFORE they will deduct the money, here I am a week later and the incorrect amount was deducted from my account after I have explained to Cell C that Barend at the branch sold me a data contract on 14 December 15 which wasn't working on my phone, (I then cancelled the contract on 19 Dec 15 - Barend re-assured me that Cell C will not charge a connection fee since it was cancelled within 7 days and no data was used on this SIM card). I am very disappointed in the service as a BRAND NEW CLIENT!