Data does not get carried over

I upgraded my contract about a year ago, I receive free sms, free minutes and 1 gig of data every month. A few days ago I noticed that my unused gig of data from September disappeared and I was only left with 1 gig for the new month of October. I phoned the call centre only to be told that any unused data on my contract doesn't get carried over but the free minutes and messages do. I was told very bluntly that I should go to an MTN store to have this checked. What unprofessional and lazy call centre agents u have. Not once did any of the consultants explain this to me prior to upgrading, further more this is the most ridiculous thing I've ever heard. My contract which I pay for every month does not carry over my data, so I forfeit this? I would like my data to be added back onto my contract or please reimburse me, had I known this was the case then I would have never upgraded my contract. I've been an MTN customer for over 10 years and I do not appreciate this poor service. I'm paying for something that is due to me, why carry over the other services but not my data. This is highly unacceptable especially since MTN charges such sky high prices on data.