Mtn contract

I was made an offer in November, I took a contract for the sim card and of a phone.

A lot of data they afford but i made sure to ask the guy if the data expiring because if it does I wouldn't take it. He then responded by saying no, the data Carrie's over to next month. Now I recieve SMS's stating that my unused data will expire in 48hrs.

Why so if the data is supposed to carry over? Can anyone help me get to the bottom of this on why was I sold a false product.