Vodacom data being depleted even though not used

I have experience my data being depleted even though I have not used it. This is despite the fact that I have put my settings for the applications to only update when Wi-Fi is on. I have also disabled. The background data for all the applications has been restricted. About 3 months ago, data of about 1,1 GB disappeared overnight. I woke up the next morning at it was gone. A bout 2 months later another 800 MB disappeared. Again a month ago about 400 MB got depleted even though I did not use it. This unfair treatment from Vodacom has carried on for a longer than a year not. I was on a contract and would receive exorbitant invoices for data which I have not used. I have written two reviews about Vodacom before.