Deleted data and prepaid airtime

I had airtime to the value of approx. R400 and 1,2GB of data This has been depleted overnight and when I called the MTN contact centre the agent says to me I have used all of this up. After pointing out that I have uncapped ADSL at home and work and my history has shown that on average I carry over 1GB of data a month, the agent says to me that its my fault because I have my mobile data switched on. She was unable to tell me on which site/app my data was depleted but insists that I have used it up. All of my colleagues at work have also claimed that they are experiencing the same problems. I am tired of Mobile Network providers abusing us and wiping off our balances without any proper explanation or recourse.