Try to change it through Microsoft account settings - it says the email address cannot be changed...?
Someone suggested changing it through the console itself through billing info - did, saved it - its still there listed as the one I want to use when I sign out and back in, but I still HAVE to use the first one to sign in. The console says the one Im trying to actually use doesnt exist.
I certainly dont want to lose the name I got over something so stupid... any work arounds? Am I missing something obvious?