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We have tried factory reset and that has not resolved it
Hello @bluemoon22
Did you try using Xperia Companion to perform a software repair?
Otherwise i recommend you to go to your local Sony support center so they can analyze your device 
Please, let me know how it goes
Thanks - the Software Repair made no difference
Hello again! @bluemoon22
Sorry to know that 😕
Since the problem persists and the software repair it´s done, please go to
Settings » About Phone » Support
Then, scroll down till you see "Microphone". Run the test!
Please tell me how it goes.
I have the same problem and have sent the phone in twice now for repairs at an authorised dealer and still not fixed.... When I do the microphone test it records but on phone calls the other party says that my voice is soft and unclear