Transfer land line service between accounts

Hoping someone from the phone team can help? My mother-in-law, who we live with, is eldery and doesn’t want to manage the wifi, cable and phone service any longer (getting too technical), and she made me a fully auth user on the account years ago. I was told by the local Comcast agent that the way to make me primary was to disconnect the old account and open a new one. So I did - same address, same everything, except now instead of being an authorized user I’m now the primary. I pointedly asked if our old number (which as been with Xfnity for years), would stay the same, and was told yes. 

So, I'm being told that unless one dies or is divorced, the number can't be ported. My mother-in-law isn't dead or divorced, but sitting next to me. 🙂 

She just wants to keep the phone number she's had here since 1989.

The Xfinity agent was GREAT and put in a ticket - waiting for an update, but thought maybe someone else has had this situation?

Thx!