Mtn contracts not true

We have taken a month to month contract unlimited wifi with the option to load data onto our phones from the wifi. This was great but we had to change from vodacom to mtn 6 months down the line we are unabke to load data and Mtn replies with we no longer support the data option No warning that this is going to happen And how can they go back on the contract we have signed up for. Im going back to vodacom as Mtn is reeling people in with empty contracts