Iphone 4s volume control button not working

Hi,

The volume buttons on my iPhone 4s have stopped working.

When I press them, the volume logo appears, but the sliding dots which display whether you are turning the volume up or down have dissapeared???

When someone rings me, I can hear it, bit not when i receive a text.

The mute button is off.

It seems weird that the icon will display, when I press either volume up or volume down, but its not displaying fully ???? can anyne help me with this ???

Thanks

Sam