Need cable rerun and buried underground

Our xfinity wire running along our house was attached to our trim and is dislodged, swinging in the wind and hitting our windows. Instead of just reattaching it, we instead want it buried underground. The cable isn’t long enough to do that now, so it needs replaced. 
I went to the Xfinity store, explained this to them and they scheduled a tech to come out today. The tech was from a 3rd party, and upon speaking to his supervisor, informed me that buying the cable isn’t something they do. Instead, they directed me to work with HelloTech. When I went to schedule a service with them, they explicitly states they do not provide underground burial. How do I get the right people out here to run a new line along the foundation, burying the wire?