Internet Activation - Modem Not Recognized

I recently signed up for service and am having trouble activating the internet via a 3rd party modem. Going through the self-install steps, I end up on a page that's telling me to call 1-800-XFINITY because my device isn't recognized. (Note: I've used this device for the last 2 years at a different address without issue).

Called the automated line, as well as the activation line and went through the automated steps to reset the connection. After multiple tries and waiting for the 10 minute power-cycle period each time, I never got confirmation that completed.

I've seen several posts here of conversations taken offline; I'm simply trying to get in touch with an actual human who can help get my service activated.