Airtime disappearing

Cell C is taking a lot of data and airtime from customers, so many people I interact with that use this network have all complained that airtime has been deducting during intervals in the day. I've seen it myself with their phones. I'd like an investigation done as I've preloaded my phone with airtime twice plus receiving my monthly R200 to use for voice and data. How can I be on day 5 for the months and every time I check balance there always seems to be a decrement in the value. I am mostly connected to WiFi and make very few phone calls, I'd like an analysis done on my contract. Can someone please assist.