Frustrated customer

I disabled my Mobile data as we use WiFi at work, but every time i check my Current usage it keeps on increasing. i mean what the ****. i understand that if my Mobile data is enabled and i use facebook or whatsupp, it should increase of which i don't have a problem. but my frustration is why does my current usage increase when i disabled the data and use WiFi? I called Cell C and they are unable to explain why and what's causing this to increase and to it up, they send me a different usage than what i am seeing when i check via *101# it's actually more than what i am seeing on my phone. May be they are charging me more cause it's a contract not a pay as you Go. Not renewing my contract with them when it expires