How do I avoid being re-directed to a different website when logging in in Safari?

When I attempt to login to AT&T's website, I get their login page, but when I enter my user ID and password I get switched to Direct TV's website. This started after I added Direct TV as a website. This only happens on my iMac and only in Safari. If I use Firefox or login from my Apple laptop, it does not happen. Back in February, John Galt gave me a series of suggestions. I tried all, including moving ~Library/Safari to the desktop. Nothing fixed the problem. Does anyone have any other ideas?