How to know Wifi-Calling is being used (Android 7.0)?

Hello, I have a S7 with Android 7.0, and WIFI-Calling is turned on. I can pick between "Wi-Fi preferred" and "mobile network preferred", and I've chosen "Wi-Fi preffered". How do I know that calls are actually going through the wifi? If there was an option to just turn off regular phone signal, I'd find out, but there isn't. I've seen pictures of S7-screens with a symbol of a wifi and a phone together, but no such symbol is showing. Should the symbol be showing on my phone, or was it taken...

How to know Wifi-Calling is being used (Android 7.0)?

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