Telkom - Contract Dispute

I received a call from a Telkom sales agent offering me a deal to upgrade my current contract plan. I enquired if this would in any way affect my current contract and she said that the only implication would be to my current subscription fee by R50. I agreed to this. A month later I was debited almost three times my normal debit. When I queried this with Telkom I was told they had to buy out my old contract since it had not expired and that there were service and admin charges associated with the upgrade. I referred them to the telephone conversation where none of this information was shared despite my asking. The only option offered was to cancel the whole contract but that also has a cancelation fee.