Unauthorised debit

In July 2017 I wanted to cancel my vodacom contract, as they did not have a good deal with the P10lite. I could get the phone with Telkom Mobile for R269 including 1 GB and 100 mins. Pumeza in the retentions department offered me the same deal R269 for 24 months, including 2GB free per month plus R200 credit for 24 months. She confirmed this telephonically on 31 July when I did the upgrade. All has been in order, but in December my invoice was suddenly R305??? I tried to query this with the accounts department who first advised me that it was due to the fact that they hadn't been adding VAT for a few months. I advised that it was not acceptable, the amount agreed upon was R269 for 24 months. I have spoken to various departments and each department gives me a different explanation. The latest is that the additional R70 discount was only for 3 months.....but that is not what was agreed upon.......Please could someone look into this, as I will be taking this matter further with the Consumer protection act, as my rights as a consumer have been infringed upon and this is not legal.....Vodacom can't just change the amount. I would have never accepted this offer if I could accept a deal with Vodacom Mobile for R269 for 24 months. Please get back to me with an acceptable solution.