It not unusual for the receive and transmit light to blink. The modem when powered up is in constant communication with the Hughes Gateway.
That "overhead" data is not charged against your allowance.
It is possible that data is being used by one or more devices on your network without your knowledge.
Routers themselves can use data depending on their internal settings. Data can be used by nearby devices if guest accounts are not disabled. Wireless devices can connect to your network if all wireless frequencies have not had proper wireless encryption enabled.
There has been a report by one user that a computer that had its normal internet connection disabled was able to reconnect to the network by using a wireless printer as an access point.
Finally we have the question of "are the devices really OFF or are they in sleep or hibernate mode"
Besides starting a new thread of your own so that support can be focused on your issue I would suggest that you run a modem isolation test to rule out any possible issues with the modem itself.
Here is the procedure:
Once you have started your own topic and have posted the results of the above test we can determine the next step to be taken.