Apple TV app looping me back to activation screen repeatedly

Unlike all the other apps I access through Xfinity, the Apple TV app doesn't activate properly on my TV. I follow all the steps to sign into my Apple TV account, and if I go to my PC, I can see that Apple knows my TV by "name" and model. But every time I enter the code provided successfully via my cell or PC and wait for the TV screen to "refresh," I'm told to enter my Apple password. And when I click the "Sign In" icon via my remote...it sends me BACK to the activation screen. So I can't enter my password. And I've started over and over and over and over again...entering countless codes...and I still can't watch Apple TV via Xfinity. What's going on? How do I fix this?