Apple TV with Xfinity Stream app

I installed Apple TV and linked it to my Visio TV.  I registered my Xfinity account in Apple TV but I cannot see any live channels,  Example:  I can watch NBC news on Apple TV but it’s a day old version.   I can watch live NBC on the iPad but not on Apple TV.

What do I neeed to do to watch live TV on Apple TV?

thank you, 

Ken