Why when my phone is on silent, i still hear the camera sound

This would indicate that the phone is from a region where silencing the camera shutter sound is not permitted to be silenced. This restriction can not be overcome.

The camera shutter sound can not be muted on device made for some markets (Japan, for example).

Because you have a phone intended for a country where it is illegal to suppress a shutter sound. Japan, Korea or Macau.