Login redirects to DirecTV - someone HELP!

I am the custodian for my 93 y/o father.  He is nearly blind and in a nursing home, so I handle all of his affairs including taking over monitoring his email for important correspondence.  I noticed months ago that every time I tried to log into his AT&T account, it would constantly redirect me to the DirecTV site (he has DirecTV, since his large screen TV is the only thing he can sort of see anymore).  I shelved the login problem until today, when I got a new laptop and was prompted to "link" all of my personal AT&T emails (I have 3) to only use one password.  I included my Dad's email in the linking process, and now I get redirected to DirecTV when I try to log into ANY of those four emails, three of which are mine.  I spent hours on the phone today with AT&T and DirecTV, multiple departments.  The only thing they could tell me is that my Dad's AT&T account needs to be "unlinked" with his DirecTV account to rectify this conflict.  But after four hours, no one could figure out how or who can do it.  I see many other threads of customers experiencing this same problem, but no viable solutions.  I would be eternally grateful if someone could steer me in the right direction.  This is a brand new computer, so clearing cache isn't the solution.  I also tried multiple browsers, my tablet and my phone with the same results.