Poor service from mtn

Last month on the 24 of april i went into a mtn store and upgraded my 2 data contracts.it was the mtn 80 50 gigs anytime and 30 night,but when i got my data it was only 10 anytime gigs while the other number is correct,and i am being billed the full amount,after several visits to stores and numerous phone calls the problem is not resolved,i will have no choice but to cancel my contract its been 2 weeks now.