bad sound quality when calling or recieving phone calls

I recently droped my phone and the screen, digitizer, and their cables came apart and ripped off! Not surprisingly, I ordered a new set of digitizer, home button, camera, sensor, earpiece speaker, all connected together so that I won't have the problem of connecting them. After installation and when I was happy with the phone cuz everything was working I realized I am not capable of doinG phone calls due to a very loud noise that comes to the speaker after a few seconds of continuing the phone call! I tride puing it on speaker, using headphones, and bluetooth headset, no luck; the sound is coming to all of them; I tried calling using viber, and textnow apps and realized the set I ordered is ok! I then however switched the whole thing again with a working 5c and still had my problem with mine (using the digitizer that I'm sure is alright). I contacted Apple and they told me that it is antenna problem and my phone is not put togeather correctly so something is touching my antenna and that's why everything is ok on WiFi!!! Please help me fix it; where is that antenna placed? What should I do?