Mtn contract -Incorrect data allocated

I recently upgraded my mtn contract. But am not getting what we agreed on. This is the third month. I have called customer care several times but they keep on saying they logged my complain. I have to get 28gig in total but I only receive 18gig. Customer care agent confirmed with me that I must get 28gig. 14gig anytime data and 14gig night. My allocation date is on the 12th. When I call on the 12th they said I must wait 24hours. After that time I still don’t get anything.