Earpiece Speaker not working after update / screen replacement

Hi guys

I have a customers iPhone 6 here, where we had done the screen on the phone. We ran function tests on the phone, and the earpiece speaker was working correctly, and I can vouch for that. The customer has said that the night they collected the phone, they updated the phone then the earpiece stopped working afterwards. I have changed and tested both the Light Sensor Flex and the Earpiece speaker but to no avail.

I have since restored the phone 4/5 times to see if it was a software glitch but it hasn't worked again

Any ideas that anyone can give me?

Cheers