20GB - 12.5GB = 0GB ?

I subscribed for the monthly 20gb contract, used 12,5gb this month, but have been left with 0gb for a few days now. How? Called Vodacom on. They logged a service complaint (for the second time - after waiting for a week for feedback from the first) and cannot do anything to assist their customer (me) in the meantime. Very frustrating!

I always thought that Vodacom was the top cellular service provider, since back in the day they're signal worked the best in my town. I was overly excited about the data deals they offered last year and I jumped at the opportunity, buying the 20gb daytime plus 20gb night owl (whoop whoop) bundle.

To a great extend I took the contract because Vodacom always seemed like a quality brand. Yet now, I am experiencing problems which Vodacom customer service is not solving and/or getting back to me about, after calling them three times!

I told them: My Vodacom app indicates that I have used 12.5gb so far this month. Yet on the same app, it shows that I have 0kb left. Should it not be 7,5gb left? Or is the app seriously flawed? PS I am giving two stars because the signal quality is good over here... Just wish I could use it