i remember when i had billing issues in the past, i tried to enter a different credit card number and kept getting that error. when i called SE, the guy said the billing servers are always in chaos at the beginning of every month cause that's when everyone is checking their bill or trying to change it.
so as dumb as this is... if you wait a few days to enter your info it should work fine, or you can also just keep spamming it and you may get lucky.(sorry, i don't think this is answering the OP, but saw a bunch of posts saying they had this problem, so yea)