Samsung S5 w/6.0.1 cann't connect to router to use wifi calling

[AC Question]

AT&T spent 5 hrs, and could not get it to work. Same with 2nd S5. Sent a Microcell. That won't work with the S5. Have been told outside that S5 will not work with either. Told I need a S7 to get WiFi calling. Any input?