What exactly does "doesn't help" mean?
What happens or does not happen?
If you go to https://customer.xfinity.com/activate-apple-tv-plus
Does it say Apple TV+ is active?
Have you then linked your Xfinity account to your Apple Account so it can link the Apple TV+ subscription?
Once the activation is complete on the above website, it should tell you to go to tv.apple.com. Where you can enter your Apple Account and link the subscription.
https://forums.xfinity.com/conversations/xfinity-stream-website/streamsaver/66607eb41e56d61567f8f90e?commentId=666326bd1e56d61567f964f1&replyId=6663411b09e34b487ca28d44
Once everything is correctly linked, you just need to log in with your Apple Account to the Apple TV+ app on your TV.