A couple notes about data usage that may be helpful:
1.) Data usage will not be calculated until the end of a session and will not be reflected on the usage meter until about 15 minutes later, under normal conditions; however, there can be delays that cause data usage to be reflected several hours later, rather than the usual 15 minutes.
2.) There is a usage counter in your mobile hotspot admin screen that may be of help. The usage counter has to be manually reset by you, and it is not tied to T-Mobile billing, but it is an additional method to monitor data usage real time and will provide a fairly good approximation of your actual usage.
Hope this helps.
i just got my 4G hotspot today and i can't figure out the math either, the datestamp of the receipt of 19:45:32 and maybe the 15 minutes or so it took me to drive home, create a my-tmobile account and i too have already used 835MB of 1GB plan, then the next hour on customer support as they all seem to think i have been watching videos while driving to my home, one thing to note is the web gui for the Device says 755Mb wonder if they use it has a floor model or something, just impossible, my only saving grace is i took screen shots of everything so hopefully a reset tomorrow as i have to go into a store as customer support can't accept emails, else i just payed $174 for the unit and $30 for a little under 200Mb of data, what a smoking deal!!!!
Sorry to hear about that. Is it possible the device you connected your machine to recieved an automatic update, such as a windows update? Some updates for software (Java, Adobe, Antivirus, Windows, etc) - can be quite large. I am not sure if this applies to your situation, but if so, I would watch out for system updates and avoid doing those with Mobile Broadband, instead use your home broadband or a free public Wi-Fi location.