How to get my iPhone 12 Pro Max to use VoLTE sim

How can I get my iPhone 12 Pro Max to use my new VoLTE sim. Because I tried restarting my phone, turned Airplane mode turn on & off continually and even try resetting my network setting and stay my iPhone is still saying NO SERVICE. I even upgraded my iPhone to iOS 15.3.1

So for so good the VoLTE sim is working perfectly in iPhone 8plus and other android.

And why I’m still receiving NO SERVICE for my VoLTE sim on my iPhone 12pro max??