Issues with wifi-calling in iphone12

Hi All,

I am facing calling issues in iphone12. I have tried multiple troubleshooting as suggested by Apple support team which includes restoring my phone, resetting network setting, renew wifi lease, tested over multiple wifi, changed wifi service provider, and may more. But the below issues continues. It is so frustrating that an expensive Apple is not working properly for a simple Facetime or Whatsapp call, but a cheap Android works. It is embarrassing.

• Wifi calling issues -- despite my network and broadband supporting wifi calling, the wifi calling gets disconnects during the call and switch to cellular network. I have test it over multiple broadband connections and the issue still persists.
• Whatsapp calling -- after few minutes into Whatsapp calling, the call gets into reconnecting mode
• Same issue now happening with FaceTime calling

Can anyone please help?

-Deepak