IF YOU CAN SEE THIS, but you can't login because you followed the instructions to "upgrade your account" by providing a street address and that broke your login by creating a new login with the same email address than now can't be authenticated because (wait for it) the email address is being used for another account, then YOU ARE IN LUCK!
You are in luck, because you now know IT IS NOT YOU, it is sap.com messing with your head : )
WORKAROUND NUMBER 1: Switch to another browser, one you don't use very often, and login using your original credentials.
WORKAROUND NUMBER 2: ...an exercise for the reader : )
WHY DOES SCN NEED YOUR STREET ADDRESS? Who knows, who cares, you can just fill in "None Of Your Business Boulevard" like I did.
You can't get mad about this stuff, you can only laugh : )