Why would a new modem fail to adopt?

Hey there, @user_l8goou! Thank you so much for taking the time to reach out to us here on the Xfinity Forums. I am very sorry to hear about the experience with attempting to activate a new modem, it certainly is not what we want for our customers. I would be more than happy to further assist you with looking into troubleshooting further the modem, and seeing if we can bring it online. Can you please send us a DM to get started?

Please send us a direct chat message with your full name and complete service address to “Xfinity Support”. To do so, click on the chat icon located at the top right of this forum's page.

Here are the detailed steps to direct message us:

1. Click "Sign In" if necessary. 
2. Click the "Direct Messaging" icon. 
3. Click the "Start new conversation" (pencil and paper) icon. 
4. In the "To:" line, type "Xfinity Support". 
5. As you type, a drop-down list will appear. Select "Xfinity Support" from that list. 
6. An "Xfinity Support" graphic will replace the "To:" line. 
7. Type your message in the text area near the bottom of the window. 
8. Press Enter to send it.

https://forums.xfinity.com/conversations/guidelines/how-to-direct-messaging-within-the-forum/697ba1e570934d009185c514