shutter sound of camera won't turn off

i have bought a used iphone 5s from a store and did asap an update to ios 10.2.1

i discovered the shutter sound of the camera cant be turned off even when the phone is in silence mode.

with my mum her iphone 6 in ios 9 the shutter sound is gone when the phone is put in silence mode.

how do i fix this. its annoying to hear the shutter sound with every picture i take. i cant even take pictures on the street without having faces looking my way when people hear the shutter sound. no matter how low the volume of my phone is the shutter sound is always on its maximum.

i live in belgium and the phone is from belgium originally its imei is ****

<Personal Information Edited by Host>