Re: unable to access billing settings because of error on page.
Sorry to hear that you are having issues with you Adwords account. If you are unable to fix the billing error on your own. It is probably best to give the Adwords team a call. They are EXTREMELY helpful.
The link below will give you their support number. Just use the drop down to choose the country you are in. http://support.google.com/adwords/answer/1385067?hl=en
I hope you get the billing issue fixed with your Adwords account.
Stefan T. Martinez
-- Not an AdWords expert, just a student eager to learn more...