iPhone 7 microphone not working during calls, Working in everything else

Hello Apple geeks,

I am here with a quite confusing issue and want to fix it myself as I bought the phone from U.S and now I am in a third world country where is no Apple store or repair stuff. I can do all replacements myself, I have tech knowledge.

Now coming to the issue,

I have a iPhone 7 128GB in pristine new condition bought new. The issue is microphone doesn't work during calls and works on everything else, I have checked all three microphones with Voice Memo, Front and Back camera each everything sounds clear and perfect like it should, Siri works fine everything clear, even third party apps like whatsapp, viber, skype etc works absolutely fine. but during cellular calls the other person can't hear anything, even if I call or he calls. it obviously works on speaker because front earpiece microphone is used while using speaker.

I can't think of any issue tried Noise cancellation turn off on again etc, hard resetting, completely resetting from settings.

Sometimes I think of replacing the bottom charging port ribbon but I feel not doing it because I can see microphone is fine and don't want to open sealed phone.

Guide me guys what should I do.

Thanks and best regards,

I hope i find my fix here couldn't find anything on the internet sadly 😟 feeling depressed.