Allocation of less data than subscribed

I upgraded my my contract with Vodacom in December 12, 2014. In the upgrade is 1 gig data. On January 1, I was allocated 500 megabytes. It took a lot of calls to customer care before I eventually got the balance on January 5, 2014. On January 31, 2014, my balance data was a little above 700 megabytes. But by 1st February, 2014, my new balance was 1.2 gigs which means I was only allocated 500 megabytes again. I have called the customer care several times and even with a reference no *** and several promises of vodacom will call me back within 24 hrs since Sunday and subsequent repeated 24 hrs call back, I am yet to hear from anyone. Like I have repeatedly said to them, I am asking not just my balance data as I pay by debit order, but that their system should be programmed to allocate the 1 gig as per the contract and what I am being billed for. I have to use this medium as I am very irritated with having to go through from ID number, bank which I use, debit date, address, etc every time I call. I dont owe them a cent nor will they forget to debit my account by a cent. I aslo dread the thought of having to call customer care many times every month for the next 23 months.