I've just received an e-mail from TelstraClear saying I've used 7,891 additional blocks of data. Each additional block is 2GB, meaning they believe I've used about 15,800 GB in a single day - according to their meter.
Since each additional usage blocks are charged at $2.95, their stats page says I owe them about $23,280 in excess usage:
Anyone with the same problem today?