What happens when you try to turn wifi calling on? Or do you not even see the toggle in your phone settings?

What kind of phone are you using?

I use the Umidigi Android Phone. I'm using a freedom mobile before I use Wi-Fi calling, and it's totally fine. 

What happens when you try turning wifi calling on? Or do you not even see the toggle in your phone settings?

It's just a VoLTE 

Here's my screenshot 

Thanks 

There's no option like updating the home address and others

Okay that looks good. Could you try putting your phone on airplane mode, (ensure wifi is on) and then see if it will allow you to make the call?

No

Is there a website link that I can activate online?

No, wifi calling activation must be done when you have cellular signal. 

Problem Solved, I turned the Simcard to an iPhone and did the set-up things and put it back on my android phone and voilà 

Now Wi-Fi calling is up.