Is there a B&N store you can go to in person? I would go straight to customer service, state that you are having an issue with an online order, and ask to speak to a supervisor. Ask where your book is in transit, and when you can expect it. If they can't answer you, or if the book will be arriving too late, then tell them you expect a full refund. You need your money back so you have the opportunity to order the book elsewhere and receive it in a timely fashion for your class.
It's a pain, but it helps a lot to speak to someone in person. It's harder to blow off an actual person in your store than an impersonal email.
Good luck!