I had the exact same problem a week and a half ago (the payment problem, not the account not existing problem). I went to make a payment using the same CC as always and it wouldn't take it. I ended up making a manual payment over the phone.
Also, a few days back, I had to help my stepfather change his payment method as his CC was nailed by nefarious people online. It would NOT take his new form of payment, so he, too, had to call to have it changed.
Something is going goofy for some with the payment system. Hopefully my payment will go through next time.
BTW, I've been with Hughesnet for twelve years and this is the first time I've experienced this problem.
When you say the old page, do you mean this, and the old sign on page the link takes you to?
I ask because if it doesn't work for me again next month I would like to try whatever it is that worked for you.