data bundle depleted and no proper explanation

I went to the Vodacom store on 160 main street in central Johannesbur, first week of May to explain that for the past for the past 3 months, I have not changed packages and use on my 500 MG and extra 1G data plan but it has been depleting every 2 weeks and later got worse that i buy data every few days, which made no sense because I spend the whole day using free office Wifi and I only utilise my cellphone data for about 2 hours per day only on whatssApp and Instagram. I was told by Moenier De Vries that my data gets depleted because of internet usage and I needed to diactivate all applications and software upgrades so I did as told and week later I still had the same issue, on the 19th of May service request was logged, the following day I received a text that an investigation was done and found nothing wrong. I was given a free 500 MG. I was still unhappy as there was no proper explaination from the technician or breakdown of what was depleting my data because I had switched all applications off except WhatApp. I logged another call,the 8th of May and received a text again saying the data billed amounts are correct with no clear breakdown by Abdul Wahaab Patterson. I am unhappy.