I have to guess there's a bug with your B&N account. If your bank had a problem, it seems like you wouldn't be able to get the 99 cent books. It sounds very frustrating. Have you tried switching your account to a different credit card, or even switching and then switching back to the one you're using? If your account is acting up, mabye that would "reset" it and make things work better.
I don't know why they wouldn't be more helpful when you've called and be on the live chat. "I want to spend money with you but I can't." That is a problem to solve. No wonder B&N is having financial problems. I mean I know there are other issues, but customer service has to be good to compete in this world.