Data missing

I called Vodacom last Friday with a consistent problem I've experienced on the contract I've been on since the beginning of 2015. I used to be on a smart std contract with only 300MB and I'd usually only have to purchase 100 - 200 MB data extra a month as I'm on wifi at work all day and very seldom active on 4G in the evening. However, on my new contract I have about 1GB of data and it runs out quicker than my 300MB data ever did. I know how to operate my phone and all backfground apps are off after use, wifi assist is off, etc and my data is simply going missing. I've taken many screenshots and data is gone after no use and no apps open. The consultant last week agreed to get a technician call me back, but NOTHING! And still my data is running out. I've checked a few times today in wifi zone. Left home with 45MB data, no use until work wifi and a few hours later I only have 4MB left. I would like to know the reason why my data is disappearing. There are a few others experiencing the same problem. This is a very costly problem. But Vodacom does not respond to calls and queries as promised!!!