I have recently purchased a new two-in-one modem/router from Arris called the Surfboard SBG6900-AC AC1900. I read some instructions on how to activate a purchased modem and it says that once it comes online, I need to go online and go to register.xfinity.com. However, when the modem/router goes online and I try to connect to the webpage register.xfinity.com, I cannot connect. Can somebody help? Many thanks.
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 / HFC MAC address and the serial number of it handy when you call.