iPhone 13 pro max - callers cannot hear me speak on cellular calls

I'm now at the point where this (sub year-old) phone is destined for the junkyard. Last try to see if anyone knows a fix...

The phone is a UK bought iPhone 13 pro Max, using Vodafone UK as carrier. The phone is 100% ok (according to apple who've had it back for test and investigation).

When making or receiving mobile calls, the other party cannot hear me at all...as in nothing. It's not poor voice, it's no voice. I can hear them fine. Equally, apps such as WhatsApp, Facetime, Team etc all work perfectly - no problem. It's just an issue with mobile voice. this happens on both cellular and WiFi calling. I have tried all possible settings related to mobile data, voice and data, accessibility and network settings. Makes no difference. the issue persists with using just handset, airpods, third party headsets and on speakerphone. Running on latest version of iOS and every form of reset, from network settings to a full wipe has been tried, and makes no difference.

this issue started last autumn (co-incidentally about the time Apple rolled out ANC for mobile calls in the iOS update)....

Anyone got any suggestions before I bin it?

Apple say the phone is fine (it's been back to Apple for diagnostics) , and "it's a vodafone issue". Voda says its an Apple issue. I'm left with a £1200, very small, iPad. All help gratefully received.