Depends on if you want to order it directly from them as a digital download or if you are willing to go to a store or have it sent to you. I'm presuming you want to order it digitally from them though based on your comment. As to any other way of ordering it from them, you might just want to try again on a different day or something them may be having some server problems.
Cant you just try to work around that?
Use someone elses card you know, a friend or relative?
Or maybe try to work it out with Anet thru some kind of support?
IF you buy from retail, BE SURE that its pre-purchase and NOT pre-order.
Pre purchase you get to experience the game on the next Beta weekend and Possibly a Stress Test. AND you start playing it day 25 instead of 28.