If you are having trouble getting past the credit card entry page or the billing address entry page, there is a good chance the issue is your window is too zoomed in and you are prevented from seeing the bottom of the form. This is especially true if you are viewing the website a small laptop screen.
This is your problem if the billing or address entry screens look like this:
Or your address entry form looks like like this:
Note how in both cases, the "Next" or "Update" button are not visible.