The same happened to my IPhone 7. Suddenly, when I was trying to make a call I couldn’t hear and they couldn’t hear me! I did hard reset but the problem still was still there. The service informed me that they can do a repair and change the sound chip ( I am not sure if I use the proper words for the repair) and you can’t do anything else apart from that! It costs about 200€ and takes about 10 days ! They said that it is a common problem to these models and it happens mostly when the mobile reaches the 2 years! Very clever, 2 years = out of warranty!!!! I find that unacceptable and disgusting for such phones! Apple has to take over the responsibilities and stop lying, it is obviously a factory problem!!!