Hey @tiagoespinha,
Welcome to the community and thanks for taking the time to post your issue on the forums.
I’m sorry to hear of the issues that you’re having with your handset and trying to activate WiFi calling.
Have you followed this process to enable WiFi calling on your device Settings > Phone > Wi-Fi Calling.
If you have already done that and its not working Then follow these steps if you can't turn on Wi-Fi Calling or make a Wi-Fi call. Wait two minutes before you go from one step to the next.
Go to Settings > Phone > Wi-Fi Calling and make sure Wi-Fi Calling is turned on.
Restart your iPhone.
Connect to a different Wi-Fi network. Not all Wi-Fi networks work with Wi-Fi Calling.
Turn Wi-Fi Calling off and then on again.
Go to Settings > General > Transfer or Reset iPhone > Reset, and tap Reset Network Settings.
Please can you try this and let me know, if it works at all.
Regards,
Steven_L