Hi
@Kapitantutan Try performing an SMMI test and check if microphone & speaker are working well.
To entre SMMI test follow these steps:
-Open calculator press .12345+= >Select Single test => Speaker
If test fails than its hardware issue to fix that you have to take your device to nearest service center as early as possible. Don't forget to backup your important data before you submit your device to nearest service center
If test pass but the issue persists I advise to bring it to your nearest service center to get it check.