I am completely frustrated with Xfinity mobile and am considering leaving for a better carrier. I contacted support 4 days ago because me and my family want to upgrade to the galaxy A71 5g but Xfinity mobile wasn't selling them yet and I was told that I needed the IMEI NUMBERS before I could find out if they were compatible with Xfinity. The problem was I didn't have the IMEI NUMBERS. So I buy 3 UNLOCKED galaxy A71 5g's directly from Samsung. They arrived yesterday and I called Xfinity mobile support and after being on hold for 45 minutes I was told "sorry they're not compatible because Xfinity isn't selling them yet." So after MUCH frustration I request an RMA to send the UNLOCKED phones back to Samsung. Then this morning I am looking on the Xfinity mobile website for devices and NOW the galaxy A71 5g is listed for sale. So I think awesome now we can use the phones I just purchased only to be told that they are still not compatible. Really? They are UNLOCKED FROM THE FACTORY! so can you please explain to me why I cannot use the $2000 worth of phones I just purchased? You now sell the same phone. Is it just a money grab by Xfinity? I wasn't happy about it when Xfinity didn't have a contract in place to sell the A71 but at least I could understand the reason, but now that they are available from Xfinity It is the dumbest thing I've ever heard of "your FACTORY UNLOCKED phones aren't compatible with our network unless you buy it from us and then you are good to go"!
I almost got caught just like you. Turns out I could just swap the SIM cards from both the S8+ phones I was replacing. I believe this is a little known/used hack (at least for Xfinity). The IMEI checker is a joke. I pluggede in the IMEI for my S8+ (already in use on XM) and it was also flagged as incompatible. So far the only draw back is that you can't manage the devices from the Xfinity Mobile app... BFD... as I also own my own modem and router and am in the same situation there. Maybe they're learning maybe we fell through opposite cracks.