Hello BeckyKo,
Thanks for that info and for choosing the Apple Support Communities. If we understand correctly, you are unable to get the Apple TV app to work on your Xfinity cable box. To help with this, please see if these steps help:
1. "In the Apple TV app
, navigate to Settings.
2. Go to Reset, then select Reset.
Resetting the Apple TV app restores it to original settings and removes your personal information, TV shows, and movies from the smart TV."
And that is from this Apple resource: Reset the Apple TV app - Apple Support If this isn't helpful, please contact Apple directly for further investigation: Apple Support
Cheers!