If all else fails, then you can try to improve your phone’s Wi-Fi performance by resetting the Internet settings. This is an option best reserved as a last resort, as resetting the network settings will remove any existing wireless settings such as VPN settings, saved Bluetooth connections, saved passwords, and more. It’s a pain to set everything up again, so make sure you’re prepared first.
A network reset can be done quickly from your phone’s Settings.
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Open your Settings app.
Scroll down and find System.
Click Reset Options.
Click Reset Wi-Fi, mobile & Bluetooth.
Click the confirm button to start the reset.
After a few minutes, your wireless settings will be deleted. After that, reconnect your Wi-Fi signal and check your Wi-Fi Calling settings to hopefully see everything turned on properly.
If this does not work, then the problem can be taken out of your hands. At this point, you should contact your wireless service provider for more information, or visit your local wireless network or authorized service center for assistance.