Trying to purchase Premium version

I’ve been trying to buy the premium version at the checkout page of yoast.com and it won’t let me. It keeps coming back with an error that it doesn’t like the state I’m in from the list. I find the state which is North Carolina so I select it and it doesn’t put a green line around the field like all the others have to indicate that info is good. I can’t find an email address to email support or call.

The page I need help with: [log in to see the link]