I had the same problem. You can email customer service off the home page, but here's the deal.
1. Change your address.
2. Notice address has the same no-changes problem--you can't!
3. Change your country to some other country.
4. Change your country back to your real country. Now you can update your address.
5. Update address even if there are no changes -- add an extra space or something so the software is fooled into thinking you changed something and save.
6. Now you can update your payment information
You probably think I'm making this up, but I'm not.