False advertising and poor after sales service

The home data contract was sold to me at R399 fixed for the duration of the contract. As we speak, I am paying R659 per month, and no one from MTN can explain to me as why this is the case. I have tried to call on several occasions, and I am not winning. All I want is my refund for all the discrepancies because the only reason I agreed to the contract was because of the price.