False Adverting and breach of contract

A cellphone contract was sold to me over the phone. The deal was 10 G of data one off included in contract and ar R12 a 1G. Data bundle Every month. After fighting with them about the 10G of once off Data they eventually told me -after me phoning them about every day- that I will niw get 1 G of data for the full term of contract which will only commence in December. Today I phoned them about the 1G of Whats App bundle now they tell me Cell C changed it to 600mb. Nobody ever phoned or let me know about any changes. What can one dobabout this problem?