Why is does my microphone barley pick up sound?

I had a faulty battery that I had to throw away and will need to buy a replacement but I doubt that would be the issue.

The microphone just one day stopped working. I could answer phone calls and I could hear them but they couldn't hear me.

I've tried turning my phone on and off, factory reset, and whatever else I could find online to try to no avail. I have also tried recording on the voice app and my voice sounds pretty low and distorted.

Please help on what I should do!

Also it's an AT&T Note 4 in the US.