C7000 cant’t find my xfinity wifi

> I bought a cable/modem router to use with my xfinity internet [...]

   Ok.  Did you mention this to the Xfinity folks?

> [...] I activated my wifi, [...]

   I don't know what that means.  What about "wifi" needs to be
"activated"?

> [...] but the router can't find the assigned network name. [...]

   "find"?  I don't know what that means.  What, exactly, does "the
assigned network name" mean to you?

   "can't" is not a useful problem description. It does not say what
you did.  It does not say what happened when you did it.  As usual,
showing actual actions (commands) with their actual results (error
messages, LED indicators, ...) can be more helpful than vague
descriptions or interpretations.

> [...] Xfinity blocks the nonXfinity router names. [...]

   This project might make better progress if you concentrated on
describing actual events, and stopped trying to explain _why_ things
happen as they do.  Especially if you invent your own technical terms.

> [...] How can I connect the router to a network [...]

   Do you mean to the Internet (by way of Xfinity), or what?

> [...] and change the default network name and password?

   I would not expect an Internet connection to be needed to let you
configure the wireless-network settings on the C7000.

   Have you looked at the documentation for the C7000?

   Visit http://netgear.com/support , put in your model number, and look
for Documentation.  Get the User Manual (at least).  Read?

   Generally, a cable-TV ISP wants to know the MAC address of your
modem.  In some cases, an automated scheme can be used when the modem is
first connected:  Any attempt to use a web browser will take you to the
ISP's authentication web site.  Failing that, you could call the ISP,
and read the MAC address on the C7000 to the support person there.

   You could call that "activating" the modem, but it's a modem thing,
not directly related to the wireless-network stuff.