Non-binding contract

We took out a MTN Choice 10GB contract last weekend with Huawei router for a price of R339.00 per month for 24x months. The salesperson, Freddie, at the Wonderboom Junction branch advised that with this package and due to their special in April, we would receive 40GB anytime and 40GB nightime data per month. Even your brochure stated '4x the data, this month only'. We signed the contract. Upon further enquiry, it became clear that we actually are only getting 20GB anytime and 20GB nightime data per month. Now, when contacting MTN SA, Busisiwe George advised that we cannot change the contract and a new one must be taken out should we require more data. This is not in line with the Consumer Protection Act at all. We were signed up on a contract based on incorrect information provided by an MTN employee. Also, your contract itself does not state exactly how much data is included in the package. Our business has been with MTN for numerous years, with many ongoing contracts. However, getting us to sign a contract based on false information due to an employee's lack of knowledge of your products and/or clashing sources of information is not in accordance with the law. I require someone to contact me urgently regarding this matter as I will not be paying for a package I did not 'sign up for'.