This happened to me, too. But when I called CS they said they could not cancel the order because it was in process. As I pointed out, it was their fault and their website problems, but no, nothing can be done.
I must wait, open, fill out form and go to PO to send back. A nuisance! and don't mark it refused because they can't track that and you'll end up stuck with two charges and one item!
REally!