Friday morning three days until the end of the billing period we had 15gig of data as we had been going close to the full limit of 107gig we decided not to do any streaming and only use the internet if needed for a few days so we wouldn't get any extra charges. At 7pm on a Friday night we received an SMS telling us we had used all of our data. I got on to live chat and explained what was going on and after 45min I asked to get an email with my data usage, which we received - the previous two days of usage (Thursday and Friday) we had used 350meg of data, as expected. Before I went to bed I turned off all of my devices so no data would be used. Saturday morning we had received at least 50 SMS/Emails telling us we had used 40gig of data overnight. I rang Optus Saturday morning another 30 Min call to explain our concern and I was told there will be checks done before the bill is sent out and not to do anything until then. On Monday morning the end of the billing period we find out we have been charged for 45gig over our 107gig plan. We believe this is incorrect and the excessive data use and subsequent charges to be very disturbing and we are unsure what steps to take now.
There can be a substantial delay in the data usage meter and subsequently when you checked your data usage in the morning you may have used more than it stated. Is this a modem or a phone that you are using for all of your devices? Might pay to change the password in the off chance someone else is using your data.