ATT Uverse with Xfinity Internet

I recently chatted online with someone from customer support at AT&T and got the confirmation that I could use Xfinity internet with Uverse service. Now that I have set up the new internet service, I can't figure out how to connect the ethernet cable from the receiver to the new Xfinity router. Just plugging in the cables into the new router isn't working. I called technical support and they were no help. 

Any ideas?