You're right syh1699 it should be working. I have a few suggestions for you. You'll want to make sure the phone has a strong connection to your Wi-Fi as well as make sure the routers getting an internet connection.
Another thing you'll want to try is checking your Wi-Fi preferences using the link below. Check to see if it's set to Wi-Fi Prefered when you're using Wi-Fi calling.
I'm having the same issue. Just started this week.