iPhone 7 microphone disabled by iOS 14.3

iOS 14.3 disabled the microphone in my iPhone 7. I have tried an update & restore but still the microphone does not work. Apple has run some diagnostics via the internet & claim this is a hardware issue but since the phone is out of warranty I must pay for it to be repaired, they say it is a coincidence that the microphone stopped working when iOS 14.3 was installed (the phone is in excellent condition). Looking through this forum I can see several other people have had their microphone disabled by updating their iPhone operating system. In my opinion irrespective of my iPhone being out of warranty the act of upgrading to iOS 14.3 caused my microphone to no longer work & therefore Apple should repair my iPhone free of charge. How can I resolve this issue and get my microphone fixed for free or working again?