Hi, I'm Robert and I'll be helping you with your computer question.
if you can get onto the page from a computer
click the name of the page ( to the right of the home button)
the part after facebook.com in the address bar is the id of the page.
you can use that to sign in instead of the email address
see screenshot below
if you are getting in on an android phone
go to settings / accounts / facebook
that also will show you the id or email that you can use as the login for the page