iphone 7 call quality poor

Hi, am facing this issue since I bought the new phone, I am told by multiple people that my voice on other side breaks and its muffled, I also got my phone changed however its still causing the same issues, I also changed my carrier sim card but didn't work, Apple needs to do something about it -not sure if its software issue or hardware to blame- hope its software stuff to get it fixed with bug fixing...Anyone else having this issue?