MISSING AIRTIME - LITERALLY

It appears when you go to bed, ur airtime literally disappears! On Saturday night I went to bed having over R100 airtime, when I woke up on Sunday and checked my airtime balance I had R0.00 AIRTIME! I called vodacom and they indicated that apparently I was on the internet. So i asked them which sites I was on or for how long ? They were not able to give me any indication of which sites I had \apparently gone to whilst I was sleeping"or for what duration of time. I actually feel like I was **********. How is it that I still had data available to me but my airtime was finished? I asked the agent if they get calls like this often and she said yes! So i asked her what exactly is vodacom doing about it??? She says unfortunately we cant do anything!!!<br> <br> THIS IS JUST A *******!"""