Why do I have so much trouble logging in?

I got a call that offered me starz. I finally accepted so I went on to the site to check the channels and any time I try to log in to my directv account it says I must be using my ATT credentials. I am not and I use a password manager so I am 100% sure I'm using the correct log-in. In fact I was just logged in recently using the same exact username and password. I have trouble with the site every single time I use it but usually it's after I log in. Is it just me? I've had directv and att for years and so far never was able to get through the site without a problem. It's not making me want to continue with directv to be honest.