Unlocked Galaxy S8+ purchased directly from Samsung isn't compatible???

Removed by me for violating forum guidelinesOk - this is very frustrating.  I literally just switched my home internet service to Xfinity JUST SO THAT I CAN BE ELIGIBLE FOR XFINITY MOBILE.  I take my Samsung Galaxy S8+ (model #SM-G955U1) to my local Xfinity store and I'm told it's not compatible.  What??? It's unlocked, I've used it on both Sprint (CDMA) and T-Mobile (GSM) through my current MVNO, and it's an S8+ - which is supposed to be supported.    I called customer service and the rep had no idea why it wasn't showing up.  He said he'd look into it and get back to me, but I haven't heard anything, yet.  He claims they just got Samsung in their system this week, so maybe that's the problem.  Is he full of it or is this the truth?  Should I expect to have it working within the next few days?