First, I would advise that you NOT cut the satellite dish off the roof and push it off into the yard, unless you want to pay for damaged equipment that you will absolutely be responsible for paying. Secondly, I advise you wait for the advice that will be given to you by HughesNet representative. You're certainly free to stop payment, but you're also free to reap the rewards with doing so, like dings to your credit, if that's what you wish.
When you cancel your service a return equipment kit will be sent to you so that you can send back the modem, the power pack for the modem and the radio from the dish. The kit will include instructions for removing the radio from the dish.
Lastly, if your DirecTV receiver is connected to your HughesNet modem it's very likely that this is what's burning through your data so quickly. Connecting a satellite TV receiver to HughesNet is advised against because of this.
The reps are normally on M-F from approximately 8AM to 5PM EST. They should reply within a day or two.