Loud speaker not working and outher speakers not working!

Replaced a screen on an iPhone 7+. Had no service so unable to make a test call. Didn’t really think too much about it. The customer picked up and called me later saying that their earpiece and lower mic were not working. I told them I was not able to test it because of no service and to bring it back when service is on. I was thinking OK, maybe I tore the front camera flex. Easy fix. Yah right. Their ear piece and lower mic do not work. The proximity sensor does not work . Also their loudspeaker is grayed out when making calls. Tried new screens, new cables. Got it working once then it stopped working and that’s that. Last resort did a backup and reset the phone with new parts on it. Same problem. Of course the customer states it was working prior, so long story short, I just bought an iPhone. The phone had the latest IOS. I read that and kind of remember IOS 11.3 causing these same issues. Can issues reside until new parts are thrown on or did the IC Chip just fail in hands. Any feedback and help for the future. I guess this is kind of my fault for not fully testing. Thanks in advance