WIFI package

After numerous phonecalls, a reference number and speaking to a Vodac9m consultant, they still haven't answered anything about my query. I have a vodacom wifi package with Vodacom (100GB day and 100GB night) @ R499.00 pm.... On my Vodacom app it shows that I have used 15GB of data from the 1st July up to date. Which OKAY that is about the usage we use. On my availability it show I have 57GB left. So if any normal human being do the math 57 + 15 = 72GB (CORRECT) So WHHHHYYYYYY can't Vodacom tell me where the balance of 28GB is that wasn't used , as it doesn't show under "usage" and is not available, as it doesn't show under my "availability"....... I am disgusted with Vodacom and their service. This is not the first month it happens. What is happening to the people's data who doesn't keep track of it???? You just ***** from them as well??? You expect your payments EVERY MONTH but you do not deliver the service. Vodacom you are disappointing!!! One of the best networks also going down the drain!