Data dissapearing

Hi,

I receive 1GB data at the start of every month, and then I add extra data as the month goes on. My data just disappear and when I call Vodacom they say it is something on my phone that is using up all my data.

I received my 1GB data on the 1st of October last night before I went to bed I had over 800MB of data left on my phone I have switched all my apps off so that it does not use data accept for my what's app messenger. This morning when I woke up I had a message on my phone saying that I have less than 149 MD data remaining on my phone?

How is this possible? It is definitely not something on my phone that is using my data as this is a regular occurrence and I have since my last complaint to Vodacom were they where unable to assist or even try to help me with the issue switched all my apps to not using data. I only switch them on when I want to use the app.

I am so frustrated as I have been with Vodacom for so many years but lately the data don't last or it just disappears and no one is able to assist me with this issue...

I want answers and if this does not stop I will not continue with any of my contract with Vodacom.