Moved service to new address, activated modem but no connectivity.

I recently moved to a new address in a different town about 10 miles away. The prior occupant of my new house had Xfinity internet and had not problems with it. He had a modem connected to a cable outlet that is on a single run back to the main line outside, without any splitters. I have 400 mb service ordered. I attached my new cable modem to that outlet and after multiple chats with the Xfinity bot and then with actual customer service people I was told that my modem was too old a model They could see the modem and reset it but there was Very slow connectivity (websites would not load at all). The said I should go to the Xfinity store and exchange it for an Xb6 modem. The guy at the Xfinity store initially said that he was not allowed to do that, but eventually decided it was ok and gave me and Xb8 modem. The Xfinity CS reps were able to reach that modem, reset it, and reassign the SSID and password. I then could connect my phone wirelessly to the modem but I wouldn't get any connectivity.  They are now sending out a tech next week. I don't think it's a wiring probem. I can't get to a higher level of customer service on the phone at Comcast due to their customer service "firewall". 

Any suggestions?

JH