My old modem Arris TG1682G lost connection, Xfinity send me a new one. I use Xfinity app to activate it. still no connection.

Try calling 1-855-652-3446. That is their device activation line.

If that doesn't work for you, you can call 1-800-comcast and tell a rep that you would like to have a new modem provisioned for service. Have the RF / CM / HFC MAC address and the serial number of it handy when you call.

Hi there, @user_b00a2b, thank you for taking the time to post on our Xfinity Forums. I am just touching base with you to see if you were able to get the new modem activated. If you are still experiencing an issue please reach back out to us here at anytime!