SBCGlobal Account Is Gone

My sbcglobal.net account seems to be gone completely.  I got emails up through Friday last week at noon.  Then I got a notification on my cell phone that I needed to re-enter the password.  I went to the settings (accounts) on my phone and entered the password.  That did not work and it opened up a sign on screen for att.net.  I logged on there but it did not recognize my user name (which is my email address).  I've tried logging on via the yahoo.com site (what I usually do) via a laptop computer and I get the same results.  It's as if my account has been deleted.