Oukitel U25 Pro Microphone issues

Hello,

I since the latest Firmware update I have issues with my device: The microphone is working improperly (voice recording, calls both by internet and telephone) and sometimes it stops working. I did a factory reset and run the phone in the safe mode, but without any success. I flashed the official Stock ROM that was available by in the internet with the SP flash tool, but even this measure wasn`t successful. I tried to enter the MTK engineering mode both by code and app but unfortunately this function is blocked (I already had the same problems before I changed the ROM). I read that you can adjust the microphone values if you use the engineering mode. Unfortunately I didn`t receive any support from the supplier and Oukitel didn`t answer my questions. 

I`m looking forward to hear from you.