Vodacom adds additional cost to contract wothout consent

Vodacom called me to ask me if I would like to consider changing the structure of my contract. My contract gives me 50 minutes and 600MB plus SMSs. They told me they found people don't use SMSs therefore would like to take away the SMSs and give me data and minutes at no additional cost to me. After I confirmed there won't be an extra cost to me I agreed. 2 weeks later I got another call asking me the same thing. The lady told me the previous person did not update it on the system. I again confirmed no additional cost.

However a few days later I received an email from Vodacom detailsing my new amount.

I went to the store and I was told to call in.

I won't call in. I just won't pay my contract. If they want their money then they can call me since they ****.