Callers cant hear me

In the last week people who call me cannot hear me. I can usually hear them. It happens intermittently. Sprint (now T-Mobile) denied it was their problem. I worked with apple to get a new device and received it today. After set up and activation I am experiencing the same problem,

I see that others on thIs chat have had the same problem. How was it resolved?  I am about to cancel my contract and go with another carrier if there is no resolution 

I have a second generation IPhone SE