1GB data missing!

My contract includes 1.3GB of data per month. Today is the third day of the month. I was busy cooking with my phone lying locked next to me, when I received an sms saying my data bundle had run out. I was aware of approximately 300MB that I had used so far, but 1.3GB FINISHED when I had not even touched my phone?? We contacted Vodacom, who refused to give out any information on where the data went because we need to pay for itemised billing monthly. (I NEVER USE THIS, I ONLY NEED INFORMATION THIS ONE TIME IS THAT NOT WHAT CALL CENTRES ARE FOR???) My phone (in data usage) says I used 358MB. Vodacom call centre says I am out, and will not explain it. I now need to buy another gig to use for the month BECAUSE MINE HAS DISAPPEARED. This is absolutely unacceptable!!!