Try contacting iTunes Support about the credit card problem. That may solve the sign in problem. When asked to sign in with your Apple ID, are you signed into iCloud? Scroll to the bottom of the page in the 2nd link. Follow through the screens to get a chat or telephone option.
iTunes Support – world wide
Go to Finder and select your user/home folder. With that Finder window as the front window, either select Finder/View/Show View options or go command - J. When the View options opens, check ’Show Library Folder’. That should make your user library folder visible in your user/home folder. Select Library. Move the following to the Trash and restart.
Close all running apps. Put the following items in the trash:
1) In the ~/Library/ folder, put the Caches folder in the trash.
2) In the ~/Library/Application Support/ folder, put the folder iCloud in the trash.
3) In the ~/Library/Preferences/ folder, put the file MobileMeAccounts.plist in the trash.
Learned fromKurt Lang