mic doesn't work while calling.

Dear team ,

This is GULSHAN SHRIVASTAV one of currently iPhone user I've brought a new one before a while and soon after a while felt it has an software error that I am not audible to the audience whom I'm calling to they're unable to here my voice while I'm using speaker mode and seems fine when I turn loudspeaker on I've changed my carrier and been in your services center twice but unable to fine any resolution since they are incompetent to find the causes request you to kindly suggest the needful and make this work again.