Wifi calling on AT&T

I am on AT&T but have poor coverage at the house so they gave me a microcell. It was fine but now they are not supporting the microcell anymore.

They say I should use calling over wifi. The other phone in the house is an iPhone and it is working fine.

I have told the Teracube to do wifi calling, and nothing is happening. If the phone will only work the few hours a week I leave the house this is not going to work out.

Also I can’t seem to find the place in the settings where the wifi calling happens so every time I try to change it I have to use the search feature, and if I foolishly push the back button, it takes me back to the front of settings not just one level up so I can’t get back easily and have to search again.

So where is the link for wifi calling naturally living?
What do I have to do to make it turn on?

AT&T supports wifi calling only on AT&T branded phones (and iPhones). Teracube will not get wifi calling on AT&T even though the setting is there.