Sounds like the programming code you used is not complete for your receiver. You may want to get a remote decoder [https://www.amazon.com/Generic-Tv-Remote-Control-Decoder/dp/B00PP6GRPG|Generic Universal Tv Ir Remote Control Decoder Tester Infrared Remote Control Testing]
Then manually create your own remote controller program for your Xfinity remote. That is if you can program it manually, I haven’t done the X-15 remote so I’m not sure if that’s an option.