Unexplained loss of data

For the past 3 months my 1Gig of data has been running up before the month is over and I have to purchase more data so that I am not charged out of bundle data charges. On Wednesday, 23-05-2018, I got a notification advising my data has run out. What I normally do, is I put my Mobile data off, purchase data from the Vodacom store and then re-enable my data once I receive confirmation advising my data has been topped up. I did this & then received an SMS from Vodacom stating my out of bundle data usage is currently R13.62. I called Vodacom & spoke to Ntabiseng who was very helpful. Unfortunately we came to no solution after she advised me to deactivate certain apps on my phone which uses background data. This I had done ages ago so it did not help my current issue of being charged for data when my mobile data was off. There were no pending videos I was receiving nor was I on any site or steaming any media. I literally only use Whatsapp on a daily basis & I can't believe it uses so much data. On Friday, the 100MB I purchased on Wednesday was done. I purchased data again. Last night again, my data ran out. This is not normal & i havent added any new apps to my phone or purcased any software. I did not de-activate my mobile data. This morning I noticed that I was unable to send or receive messages on Whatsapp not was I able to send or receive emails from my phone. However on my Mobile Data graph it showed I used 14MB worth of data. How is that possible? I called into Vodacom explaining my situation, the consultant this time around was very unhelpful. She also advised de-activating the background data for certain apps. She refreshed my SIM & advised me to reboot my phone. I am still unable to use any applications that require Mobile data. She was supposed to transfer me to the Solutions department, but disconnected the call instead. Wow...

Where has my data gone to? Vodacom just charges their consumers without giving any reasons as to where the data goes. Vodacom was supposed to be my service provider, but cannot answer any reasonable questions concerning their own network services.