iphone 4s not ringing but receiving calls, no sound notifications evident

My iphone 4s receives calls but has stopped ringing, hence I keep missing calls. I have checked my settings, the volume is up and it is not set to silent. I have always had the settings so that it rings and vibrates together, itrs just stopped ringing.

I have been back through ring tones and clicked on it and it sounds, the speaker works also. It would seem all announcement tones have stopped announcing be it text, call, message etc etc.

Its doing my nut in as I I am missing lots of important calls and am finding I spending a lot of my time checking my phone for missed calls.

Any ideas anyone?????