The charges are probably done automatically, so no person needs to be there. And yes, it's unfortunate that this happened on a long weekend.
I paid for the first month of service when I cancelled as well.
This is normal, as it's forward billing. In other words, you're paying for the new month, not the month you just used.
HughesNet doesn't charge "however much they like." They charge the fees set forth in the Terms of Service and Subscriber Agreement.
On a side note, if it was a lease, I hope you still have the modem, the power pack for the modem, and the radio from the dish, as they will want these back.
Welcome to the community and thank you for posting. As you were informed by one of our agents over the weekend, it's best to contact the business support line 1-800-347-3272, as they have the means to address your concerns. The community is geared toward residential customers, so our capabilities differ from the SME agents.
Your cooperation, patience, and understanding are much appreciated.