Well, then try FP direct. @Esmee already offered her help.
There might have been a faulty batch of microphones (it really looks like it). Should PhoneCoop have got their share of this batch, it is likely, the repair attempts result in another breaking micro.
You seem to have “hit the jackpot” with your phone.
On behalf of the seemingly high failure rate of FP, I have put my thoughts down here:
I guess @langga is true in a way, seeing us customers with problems
The lack in quality control at the manufacturers might well be due to the fact, that FP is but a small customer compared to almost every other company producing smartphones. So the sorting out of faulty devices is completed by us.