Insane account billing

<p>I upgraded last month Nov 2016, today the 1st of December 2016 i recieved a debit order off R17600 for the month which is insane and cant be realistic due to the mobile data being off on my phone because i am only using wifi at home and work. My phone is 99 persent off the time connected on the wifi. I phoned vodacom customer care and they said if data that i have used. The guy that was doing my upgrade said that if the phone's data is done the phone will be locked. Apparently this is not the case. </p>