Underground cable

I have tried multiple times and spent hours on the phone with Xfinity customer service to resolve this issue with no luck.  My house is getting remodeled.  City regulations required me to change overheard electrical service so all utilities can be underground.  I paid electric company to provide underground electrical service, and when they did that the city required them to lay conduit to run the cable and phone lines underground at the same time.  So all Xfinity has to do is to pull their line underground from the utility pole to the house in the conduit that is already underground.  Every single customer service agent ignores this explanation and assumes that I am asking for Comcast to actually dig a hole and bury the cable, which is not the case.  I just need Comcast to pull a line through the existing underground conduit and remove the preexisting overheard service.  How do I get to the department that does this???