rosegravette,
As was related to you previously you can only terminate your service by phone.
The number is 866-347-3292
If you decide to cancel, your service will usually terminate at the end of your current billing period unless you demand an immediate cancelation.
When you termination date arrives you will be sent a prepaid Return Kit.
You will be required to return the Modem, Power Brick and cords and the "radio" that is mounted on the end of the dish "arm".
If you do not return the equipment you will be assessed an "equipment fee" in addition to any ETF fees you may owe.
Some details: (click for larger image)
Complete information can be found here:
http://legal.hughesnet.com/ServiceTermsAndConditions-current.cfm