No audio on incoming calls with an iPhone 12 Pro Max

Hi Team

I've been living with no audio on incoming calls for around 2 months on my iPhone 12 Pro Max. I can do a network reset and the problem goes away for a few days. I swapped my old cut-down SIM for a shiny new one a fortnight ago and that did not fix the issue. Today, I called the Vodafone Ninja Team and spoke with a gentleman in India who was good enough to listen to my troubleshooting steps before logging a ticket for the next level team to look at (rather than making me re-do the basics with him). I thanked him generously for that.

Does anyone have any suggestions to shortcut resolving this?

Cheers