sound diverted to bluetooth even though not connected to any device.

I had a customer come in with her T-mobile Galaxy S4 for a screen replacement. The screen repair went flawlessly. She later returned stating that there is no audio, incoming or outgoing, but only when in a phone call. After strenuous testing i have determined that the audio in call only works through a bluetooh device. I tried using my samsung headphones, no go. I tried swapping the motherboard, the sim card slot, the back body, charging port, speaker, and anything else you can think of to swap out for it to work. I tried turning off "OK Google", like pretty much every online thread that i read said to do. I've killed processes and gotten slight progress only to have it disappear immediately. Please someone help.