[Fish]

Sounds like you have to activate new 3rd party equipment...

Frequently Asked Questions
Can I bring my own equipment to Comcast?
You can purchase your own retail modem for use with your Xfinity Internet and/or Voice service, as long as the equipment is certified to work on our network. Before buying from the retailer of your choice, please go to mydeviceinfo.xfinity.com to find certified retail equipment that supports your Internet speed tier.

If you're an existing customer and need to know your level of service, see which level of Xfinity services you subscribe to. Then, after buying compatible retail equipment, install and activate it and start enjoying your service. To learn more, see more about installing and activating your purchased modem with Xfinity service

What are my responsibilities when buying and using my own equipment with Xfinity service?
You're responsible for making sure your retail device is secure and certified, that it supports your Xfinity Internet service speed, and for upgrading your equipment when we increase speeds. Visit mydeviceinfo.xfinity.com for compatibility.

Try the info here: https://www.xfinity.com/support/arti...-gateway-modem