Unhappy

In November I received a call from a consultant at Vodacom, advising me that they would like to migrate my account as I am receiving SMSs every month and I am not using it and they want to exchange it for airtime. My first response was will this cost me extra on my current bill and her response was no. I continued to ask are you sure as I don't want to pay extra, she said yes she is sure. Now today I received my bill for December and I am being charged extra for the migration. Phoned Vodacom immediately and they response was they can't change it now. I want it to be changed as it was not as per what we agreed upon during the call. I'll rather go back to having SMSs then to pay extra