Q: People can't hear me when talking on the phone of my iPhone 7

I recently purchased the iPhone 7 and whenever I call someone or they call me in the middle of the conversation they are not able to hear me while I can still hear them; often resulting in them hanging up on me and having to call them back only for the same situation to happen all over again; sometimes after putting the phone on speaker then turning speaker off they'll hear me again but minutes later they can not hear me again.....please help