Upgrading Voice and Data Modem and Cable Modem - Activation Help

Hello,

Our house has both a customer-owned cable modem and a rented voice and data modem.  The cable modem pre-dates the voice and data modem, which Comcast installed when converting the telephone service to VoIP. This is how the devices appear in our account:

Source: https://customer.xfinity.com/#/devices

We recently purchased a new cable modem and a new voice and data modem after experiencing a degradation in service quality. The existing modems are at least 5+ (possibly 10+) years old and are no longer supported by Comcast. The new modems are both supported and approved by Comcast/Xfinity. I believe Comcast had installed a second physical modem for the telephone service because the telephone wires in the house do not extend towards and are not near any of the in-wall coax or ethernet terminals used for the internet and cable service in the house.

What are the steps that we should take to activate the new modems? Is there a phone number we can call to speak with an agent?

From what I understand, the XFinity app will only allow us to activate one modem when two are needed for the separate services.

Many thanks!