Samsung Galaxy A57 not compatible

So i bought a galaxy A57 and only Xfinity can recognize the imei number... its a US unlocked phone bought from Samsung.  Yet i try Verizon good to go, Visable good to go, Total wireless good to go.. Even ATT and Tmobile said the phone would work... So what gives with Xfinity called tech support they said its a locked phone or it has sim restrictions.. Xfinity needs to step up their game... Does anyone have a number to a tech support person who understands unlocked cell phones... No reason they shouldnt be able to activate this phone on the network