I cant hear or be heard on my nokia 530 out of the blue, engineers say its not faulty?

[Windows Central Question]

My phone has been to O2 for repair as I can't hear or be heard when making calls, yet engineers say it is not faulty, read that it is the 8.1 update to blame, can I make it run on any other program?

 

[v535]

Did you check in-call volume level?