I did file a complaint with the FCC, who wrote me a nice email to say that they knew about the number and thank you so much for filing a complaint.  The AT&T operator told me that if the FCC gets enough complaints about a number, they will actually act on it, trying to trace it to its source, since false caller ID numbers are against the law.  So everyone, do complain.  Here is a link to the complaint form:  https://consumercomplaints.fcc.gov/hc/en-us/requests/new?ticket_form_id=39744