iPhone 12 pro max microphone issues

Microphone on my new iPhone 12 pro max stops working intermittently (person on the other side can't hear me for a fraction of a second) for all calls: whatsapp, facetime, or normal calls. Went to the nearby Apple store (I'm in Sydney, Australia) and they said they can't replace the phone, but can replace the phone components except the screen/body (found that weird). Apple web support has agreed for a replacement but not sure if I should go for it as I would end up getting a refurbished phone. Can someone here help me in having the phone replaced. I am not looking for any troubleshooting steps, as we've done that already (phone reset twice). It is frustrating as my previou $350 XIAOMI phone was far better than this $1849 phone. Regret switching to this phone.