Caller can't hear me even though the microphone works

Hi, I have a very weird problem. So basically I had Cyanogenmod on my Galaxy S3 and one day somebody called and I couldn't hear them and they couldn't hear me either. I tried turning the speaker on and it still didn't work. I thought that maybe my phone was damaged, so I tried calling somebody else on Skype. Surprisingly, it worked perfectly. I tried going back to factory setting - nothing happened. I just got my phone back to the stock OS but the problem is still there. I am completely out of ideas