It may be for something like taxes. That's not to dismiss your displeasure with a surprise billing, but that may be what it's for.
You can sign into http://my.hughesnet.com/myaccount and click on My Bill, then click on the invoice in question in Invoice History to see what the bill was for. Also, while viewing the invoice in the popup window, if you scroll down to the bottom, you can click on View Site Details on the bottom left and it will show you a complete breakdown of every single charge on that invoice.
Hope this helps.
Edit: Just to add, normally you only receive one bill each month, but this may just be playing "catch up" with your first one.
Sorry, but I can't "help undo this injustice" as I'm not an employee. I'm a customer, like you, and was only giving possibilities of what the charge could be.
Employees will have a label next to their name, like Mod, to indicate that they are employees. They're on M-F from approximately 8AM to 5PM EST, though it can take them a day or two to reply. I'm sure they'll help you.
Please accept our apologize for the inconvenience this has caused you. We cannot calculate state, local, property or communications taxes at the point of sale so customers where taxes apply will receive the charge for taxes after the system is installed and activated. This should have been explained in the welcome email sent to you after ordering. In any case, I'd be glad to assist you further through the private message you initiated.
It's been a while since we've heard from you so this thread will be closed. If you have any questions or concerns later on, feel free to create a new thread. Please note I previously sent you a private message on March 9th with more information.