Hi, I am using Sony Xperia z3, even I faced the same issue after upgrading to Android 6.0.1. First what I did is in settings-->sound & notification-->phone ringtone and selected a song , but it didnot work. So , I went to music app and selected a song and set as ringtone .... it worked. I don't know the root cause but anyway now I am getting sound for incoming calls. Hope it works for you.
... View more