I basically have the exact same question as was asked in this thread, which never got resolved.
Basically, I no longer have access to some of the devices which have a reserved IP address assigned to them, so I can no longer connect them to my Xfinitiy router to unassign those addresses. I really need to solve this problem, so help would be greatly appreciated. Really seems like comcast really messed up by not including a way to free up old reserved addresses.
I'm hoping that if nobody can help me with this, at the very least this can be escalated to someone who can fix this bug.
Thanks for using the Xfinity Forums to get help removing a reserved IP address. I'd be happy to help! Please send me a private message including your first and last name and the numbers associated with your service address. To send me a private message, click on "ComcastChe" and then click send a message.