I do apologize that you were not able to find your cable provider when putting in your zip code. The purpose of that selection is to provide you with a guide that has your channel listings within the app. You will still be able to use your guide from the virtual remote itself.
The newer set top boxes from Comcast typically use the same remote. I would advise to use the search option when selecting your set top box, and select the XR5 remote. Hope this helps!
Sling Media Moderation Team