Moved to a building that includes Xfinity. Xfinity account shows no account despite Wi-Fi working with our modem.

We previously lived in an apartment where we paid for our own Xfinity services and it was connected to our account. We cancelled that service and returned that equipment when we moved last month and picked up the new equipment for our new condo (we are renters). The owners . I repeatedly tried to set up the new service with the new equipment. Interestingly, the Wi-Fi still works when using the pre-determined password, but it shows that our account is inactive, so we can't select any upgrades. We thought it may be because the internet is included with our building, but our landlords who are previous tenants were able to connect to their Xfinity account when they lived here and cancelled their service before we moved in. How do I get the modem to connect to our account?