Porting a number from Vonage to Xfinity

Hello--I'm trying to port my Vonage number to Xfinity, and I understand this is problematic. What's interesting in my case is that the Xfinity rep couldn't even find Vonage among the list of carriers. He was wondering if Vonage has another business name he could look for. Is the issue related to these "rate centers" I've been reading about? Can anyone tell me whether it's possible to transfer a number from Vonage to Xfinity? If so, what steps should I follow? I have a transfer PIN and my account number from Vonage, and so far that has not been enough.