No volume knob on radio

[Trumpet5]

Hi new on here so bare with me. 

2016 Q7 

Randomly today ive lost sound on my radio and Bluetooth connected devices. When you use either button (center console and steering wheel) the bar comes up but it doesn’t adjust the volume. I have volume and sound on Nav. Have tried resetting MMI but no joy. Any help gratefully appreciated. the skip button works and you can mute the radio.