Why can I not be heard when receiving phone calls?

I have a B130DL BLU Android phone from Tracfone, had this for about a week, and I’m experiencing a very weird problem. When receiving phone calls, I cannot be heard by the person on the other end. I can hear them but they cannot hear me. This problem doesn’t come up when I’m the one making phone calls, and voice recording apps work fine so it’s not a microphone issue. But for whatever reason I can’t be heard when they make the call to me.