Having call issues with Samsung Galaxy S4

About a month ago my phone stopped having volume on calls. I hear the connect tone but its just silence after that. On the other end they cant hear me either. I take it to the device support center, the lady does something and it works for a few hours, but then starts having the issue again.

I have tried everything online forums have suggested, even did a system restore on the phone on Friday.

My warranty is void due to a cracked screen and I would prefer not buy a new or refurbished phone.

What are the chances I call up Samsung and claim I have a defective phone and they send me a new one? Anyone on here encountered this problem and have a solution?