Unable to switch to NOW mobile to Xfinity mobile for weeks !

Hi All,

I have been trying to move from NOW mobile to Xfinity mobile ( postpaid ) for almost last 1 month I been struggling between showroom , virtual assistance and chat assistance but no luck so far. Every time they are saying different reasons and close the ticket. Is there any way out to move my prepaid to postpaid plan within Xfinity or port in to different carrier is the only option ?