New Xfinity scam

Apparently there is a scam coming from am [Edited: "Possible malicious number"] - received an urgent call that i will be disconnected - call them back - called them back and got vm initially which seemed as if it was Xfinity -  purporting to be Xfinity offering 50% off current plan for three years.  They then say they will transfer you to billing and that it is a three year plan and will save you 50% off your current fee structure - they then say you have to prepay 20 months of the 36 month plan.