Sorry to hijack this thread but I'm having the same issue on a dudu5 for a nissan Navara
My internal mic doesn't work, but I don't care about that as they are rubbish anyway. But the external mic jack does nothing. I have tried 3 different mics and checked the wiring and the connection to the mic jack and nothing.
OP if you go to settings , about device, scroll down and you will see android settings, click that
At the top you will see box settings, click that, then scroll down to mic switch, change that to box mic. That will manually switch it to the external mic. If that doesn't work it's probably a faulty loom or unit like mine, unless someone else comes along with another way to get the mic jack working