Can't mute the camera sound in new iPhone 6?

Just got a new used iPhone 6, and can't mute the camera shutter sound. Mute button doesn't work, and when I try and adjust volume all it does is just take more pictures and make more noise. Have checked camera settings and sound settings and there seems to be nothing.

If the mute switch does not silence the camera, it means it is a model originally made for Japan or Korea.

In those countries, all phones have the "silent" camera shutter facility disabled.

Depending on where it came from that may not be an option. Japanese sold iPhones can't due to laws against that. As far as adjusting volume & it taking pictures, in more recent versions of iOS/iPhones the volume up button acts as a shutter button.

iPhones sold elsewhere can mute the camera shutter just fine.