They know who you are. They know everywhere you go. And they are happy to spread what they know about you around.
Is this something new? What was the flow? Do you have both AT&T internet + TV as well?
https://www.fiercecable.com/cable/tv-everywhere-starts-up-46...
(I also run a site-specific browsers via Chrome to isolate my Gmail login and keep Google from knowing who I am, I have no Facebook login, etc. I'm not serious enough to run a VPN or Tor, and my setup isn't enough to guard against browser fingerprinting, but I'm reasonably paranoid.)
Personally it's handy as my ISP lets me watch tv on any device on my home network. They did it badly because it breaks if I change the SSID.
But you're not truly paranoid unless you're using tor or a vpn to get away from your ISP's network. Your efforts mostly are an annoyance to yourself but no impediment to other.
I bought my dad a Roku TV for his birthday and the idea of having to go to website, login with his cable companies userid and password and then use the one time code displayed on his TV,confuses him to no end.