Can not hear the caller

[Posi1]

I recently bought a Mix 2S (MIUI 9.6 Global).
When I call someone or receive a call I can not hear the other person, only when they call a second time.
It is not a SIM card problem, as it works fine in another phone.

Did anybody else experienced that issue and would know what to do?

Many thanks

 

[Posi1]

I found a way to work around that problem: when making or answering a call I switch the phone from "normal" to speaker and back to normal. In doing that I can have a conversation without my microphone cutting out.
Would anybody have an idea why that is the case?