This is just so frustrating!  We have people who mail or bring in a bunch of registration and paying with one credit card.  And since you can do multiple registrations (another stupid issue) you have to enter them separately.  So of course they all get declined because their address does not match the billing address on the card.  You should have the option to change the billing address.  Supports answer was to register them on the front end and if they have participated in the past go in to their record manually change their password, then register them and then send them a password reset.  How ridiculous is  that and who has time!  It's things like this that I miss sphere.