I'm sorry to hear that you're having difficulties adding a billing method. Could you please clear your cache and cookies or log in with another browser? Let us know if the issue persists and we'll look further into that for you.
I have tried clearing cache, a different browser and even used my phone. The "hire" fields allow me to enter my address information, etc. but the credit card number field, the expiration date and the security number field don't allow input.