I am pretty positive that the little black piece that broke off is just a bracket that helps hold the board down. Was the front camera and earpiece working before the repair? If you don't know then make sure to try and test the components of the phone before repairing, that way you know whether or not something else was damaged before you started the repair. To me it sounds like the flex was damaged during the repair or by the customer. I would try replacing the front camera and proximity sensor. I have had times where the earpiece worked but the front camera didn't.