WHAT A ****

Took a my mtnchoice 10g contract with MTN last month on the 18th of September. The catalogue stated that I would be credited with 40g every month which is why I chose the package. When I noticed I hadn't been credited correctly last month i quickly called the sales assistant at the mtn store who helped me sign up. She dismissed me and said it's probably pro rata bundles. This month to my surprise i have been credited with 20g. Half of what I signed for. Why would MTN false advertise? I am cancelling this contract ASAP and I'll be looking for a better service provider that doesn't lie to it's customers.