I'm super confused by this process.
I'm going to be getting a new modem, and in reading up on the modem, it says disconnect old modem, attach coaxial wire, plug in power wire and let modem go through power cycle. Attach ethernet cable and plug into a laptop or other computer and activtate using the activation link. Seems simple enough.
Here's the sticky wicket. the instructions say, the modem is not activated, so no internet access will be allowed.
Question is....how do you activtate it through a website if it's not activated? The objective is to avoid calling Xfinity as the automated menu's just stink and getting a live person is more difficult than it needs to be and it took them 8 hours to activate my old modem.
Connect it to the coax line and power it up. Let it fully sync up with the system ("DS, "US", and the "Online" lights are steadily lit). Connect a computer to it and open up a browser. You *may* see their "Walled Garden" modem self registration page. If so, follow the screen prompts. Have your mobile telephone number, your Xfinity username and password or the account number and telephone number associated with your Comcast account handy.
If not, 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.
I just replaced my modem yesterday. After giving it time to fully boot up and get updated to the latest firmware, give it a few more minutes. I opened up a browser (Firefox in my case), and it mentioned having to log into the network. When I clicked accept, it came up with the Comcast screens to enter your ID. The first time I tried, it said there was nothing to activate. I tried the phone number, but got stuck in that stupid computer voice black hole. I tried online again, and this time it accepted the change and the modem rebooted and everything was working. Also, after a bit, it also showed up in my Comcast Account settings.
I can add that this is a plain modem (old was Zoom 5341J, new is Arris SB8200) with a separate router (Asus RT-68U). I just left everything connected as-is. In the past, there used to be mention of connecting directly to the modem first, but I don't think you need to do that anymore.