Calls are dropping very bad that i can't use my phone

[donmedo]

I just bought the oneplus 3t yesterday every thing was fine and i was happy but after several hours of opening it and setting every thing and making some calls calls started to drop very badly that the other person cannot hear me at all or hear my sound distorted i was pretty sure that the area has an excellent call reception by using other phones in the same exact spot, i have contacted the live support and they advised me to factory reset and if the problem still exist get it back for exchange, i did and every thing seemed fine for several hours but again the problem appeared now the problem is that i bought the phone from another country and its extremely hard to get it back for exchange is there any way to fix these problem? Help me please
By the way i suspect that a certain app could be causing the problem is that possible?

 

[ilyr73]

I had similar problems on my MotoG when I used BoldBeast call recorder, probably with a bad settings. Also if your SIM card was cut from micro or normal SIM and got damaged, it might produce such issues. Easiest way to find out is a factory reset and before you install anything, test the calls.