I sent an email to the address (
[email protected]) listed on their website (http://byersebooks.com/) and received a reply within 24 hours. (Interestingly, it was a lengthy form letter, as if they get many similar complaints.) They suggested that some shady characters might have gotten my credit card information and charged the amount on their website. But they did refund my credit card for the amount charged ($4.95). Hopefully that's the end of the story.