Charging to much after contract renewel.

During Black Friday, i updated my data contract. The consultant said that a new sim will be send to me me. I phoned later and said the sim never arrived. Then the new consultant said i will not get a sim, but they will update my contract. I said that then the new contract should start on 1 December, but i see they still billed me December on my old contract which is much more expensive.

I asked for a recording of the phone call 11 Dec, but did not get any feedback yet. I don't know what is going on and no body is getting back to me? Yet i must pay more due to Vodacom's error?