One option I used to use when abroad is to go on airplane mode to make the call (and turn wifi back on) to force wifi calling

Messages for web lets you make calls, I saved the site to my home screen to make a web app.

I have an app called GroupMe. It's actually a lot like Hangouts. You add people to the chat and anyone can see your messages.

Before the Google Fi app wouldn't use Wi-Fi well.  I'd get charged overseas for calls.  I was using hangouts and it worked well.

I still don't trust google fi to use wifi.  Is there an alternative like hangouts?  I'd rather drop the call than pay for it.

Is there an alternative to hangouts?