First and foremost, it's an impossibility for data to be used/lost during a power outage. Data absolutely cannot be used, nor lost, if the modem has no power. Either the data was used/exhausted prior to the power outage, or after the power came back on, but it is a factual impossibility for data to be used in any way while the modem has no power. Data usage is entirely reliant on the modem and its connection to the gateway, and if there is no modem power there is no power to the dish, and therefore no connection to the gateway. Whether you consider this a robotic reply or not, it's a fact.
As for your high data usage, there are a few possibilities, and I'm sure that the reps will run remote diagnostics on your HughesNet equipment (be sure to leave it plugged in) to see if there is any issue with that equipment. If they check your equipment and everything is in order, including adequate WiFi signal to your devices, the next step is finding out which apps/programs are the proper ones for your devices in order to monitor the usage of each device to find out where the data drain may be.
The reps are on M-F from approximately 8AM to 5PM EST. They usually reply within a day or two.