Q: Problem with audio during calls

There's no audio during calls placed by carrier. But when placed by whatsapp it works.. I checked if the problem lies in the sim but it works fine on other devices..

I took my device to Apple service centre they said the software is good and might be a hardware problem but couldn't exactly tell what the problem was.

here are some attached images during calls. Speaker option does show up and fails to make a call or recieve call..it rings during incoming call and when i answer it the screen stucks

help me peeps.!

iphone 5s/ A1530