missing airtime

I am a vodacom contract holder for over 9 years now. I have a top up R315 contract and a 1.5 GB data bundle contract with them. Now yesterday I had R109 in my account and at 17:57 I received a message from vodacom notifying me that I now had 4.d6MB left on my phone. I did not surf the net or anything like that. At 21:30 I wanted to make a call but the call didn't wanna go through. I check my airtime only to find that I was left with R0.01 and no data. I got confused so I checked my data usage only to find that the phone says from the 1st to the 21st I used 1.11GB not the 1.5GB. I then called customer care to find out what's happening. This lady answered I didn't get her name. I told her my problem then she said that the phone goes on the net without me promting it to that's why my airtime is finished. I told her that doesn't make sense to me as I get the same amount of airtime and data every month and this has neva happened. She said well it does. Before I hang up I did that rate the level of service thing and I rated a 0. This lady had the nerve to send me a message saying \why did you rate me a 0 if I assisted I did not take your airtime". Like what the hell.pls fix this."""