Guys
I was facing a similar problem during calls only. The mic was dead and I could only hear but to to be heared. Speaker mode and external mic (BT headset and original earphones with mic) were working perfectly.
Tried reset but didnt fixed the problem. Reading another forum discussion I heard a guy sayng that fixed the problem with a blast of compressed air. Sounded weird initially, as the mic was aparently clean, but wouldnt hurt to try it.
So I tried cleaning the mic with compressed air and a soft brush and, voila, the mic is back!!
There were no dust, moist or any dirt particle visible in the mic, but aparently, as the device is very sensible, minimal particles can affect the functionality of it.
Dont know if the problem is the same for all users, but in my case it worked perfectly and the solution was simplier than imagined.
Best,