Disappearing DATA from Vodacom Account

This has been at least the third time my data has disappeared within minutes. I am referring to hundreds of megabytes without me even being on the internet. This is not acceptable as I am not a new phone user and Vodacom treats me like something was updating or running in background as if I am not aware of what I am doing on my phone.. I would like an explanation why you cant seem to fix this glitch in your system as it is happening to so many customers...