Not adding up recurring data. Very disappointed with MTN

Very disappointed because MTN is not adding up the unused data that they are suppose to add on to the 60gig. Today on the 11th April i have 12 gig and tomorrow they are suppose to add 12 + 60gig. They have been doing this since i upgraded the contract and when i complain they tell me stories that i do not understand. All i want is for them to add my data.