Hi All,
I had exactly the same problem, I cleaned it out with a pressure cleaner.
The solution to months of trying was..
ensure the botton on the side is switched unmute then..
go to settings > general > accessibility > assitive touch.
a little dot will appear on your screen > tap it > tap device > and tap unmute
it worked for me, and finally i can hear people ringing.. however i always have to turn the acessibility button on to change from silent to loud.