In my case, Vodacom is guilty of many faults, but nothing near what you are hinting at.
The highest amount my data usage has ever been "out of sync" with reality was a 1.2% difference in upload between Vodacom and my connection monitor (a total of about 2MB of 240MB).
To add to that, it only happened once, when I was on unrestricted APN, so most likely i was getting port-scanned.