Had the same problem here...tried to make my 4th extra account and 'twas denied. Blizzard does it on their end. Just use your friend's computer...for me it was my IP not my credit card seeing as I read him the digits over the phone and it worked with no issues.

EDIT: I believe if you call them they'll make your account for you but it won't be RAF'd. You have to start the trial yourself...but maybe they've upgraded their system who knows.