Redmi note 3 problem with upper microphone

Hi everyone,
I have an huge problem with my redmi. When I make a call the microphone that works is the upper one (the mic near the jack 3.5). So when I make a call (or answer) I have to speak near the upper microphone because in the other case people can't hear me...they hear me like I'm speaking very far from the phone.

The miui installed is the original 7.3 stable. Never installed a dev or other version or Google OK (google now) app...
I always thought that redmi suffered of a poor quality in call but until today I made calls without such huge problems...

What can I do? :(


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