Port number

I relied on language on the Xfinity website regarding number porting when deciding to switch to Xfinity:  "You must establish service in the same geographical area (rate center) as your old residence. Comcast cannot port phone numbers across rate center boundaries."

I checked porting when placing the order but an agent told me to place the order with a new phone # requested, and then to request porting after installation.

Now, I am told that my number can't be ported because it crosses a rate center boundary.

It's the same address.  I have not moved.  How can this be?