Double-dipping payments on bill

It's an accounting error. But for the delayed refund, blame the banking industry, not HughesNet. 

Companies issue credits immediately. The banks themselves sit on that money for up to seven days in order to make interest on it before it's actually refunded to you. 

Only very large companies, such as Amazon, issue credits directly to their customers. Most companies, including HughesNet, go through a bank.

"you're sitting on other people's money."

Dude, I'm a subscriber. I'm not sitting on your money; neither is Hughesnet. You'll get a refund when the bank releases your money, and continuing to carp about the issue won't get you your refund any sooner.