MTN not keeping to their contract

We've had our data contract with mtn since 2014 it was a special they had for uncap data for a small amount,through the years they have phoned and tried to get us to "upgrade " to a different plan. We polity refused. Then on the 29th of December we ran out of data we just could not understand. Bottom line is that "someone " has changed our contract to a 30 g a month, we of course disputed the matter,after many calls and frustration I got to a lady that sens a email to the relevant department as this was ***** . I was then told that it will take 10 working day's for the problem to be resolved so we were without data. My husband is dependent on that data as his a musician . So then earlier this week we got a statement from mtn and I thought ok they've sorted out the ***** but o no nothing of the sort we are still on the 30g . On inquiring they said that,the plan that we were on no longer existed. We told them that it's not our problem we had a contract that we DID NOT CHANGE they have to keep to the contract. My daughter spoke to a Grant Baadjies ( hope I spelled it right) 2 Days ago up to now we didn't hear from him. Ok so now we have data we have to be very selective on how to use it because its not going to last. I FEEL IT'S NOT OUR PROBLEM MTN MUST KEEP TO THE CONTRACT