I emailed the Etsy support team about the whole credit card issue and less than two hours later I received this reply:
Thank you so much for contacting Etsy about becoming a seller. To use a ************** card, please select the Mastercard option. Please note that any card with more than 16 numerical digits will not work in Etsy's system. Please let us know if you are still having trouble registering your card, and will do everything we can to help get you started.
Now that is support!