In the same boat as an AT&T customer, and I totally agree that this is false advertising.
If you’re OK with risking an unstable solution that may break again without warning you may be able to get it to “work” by going to an AT&T store and doing what I did here: Mudita Kompakt does not work with AT&T
My plan is basically to see if I can get away with this hacky/unstable solution, and if not, just switch to T-Mobile…