I don't have this model Samsung, but on my phone:
1) Make sure ringtone is on in the settings (not mute, or vibrate). This can be checked by swiping down on the main screen and looking at the button for call notification. Change it if necessary.
2) Open the phone app. Then tap the 3 dots on the right.
3) Pick Settings in the popup menu.
4) Scroll down to Voicemail and tap on it.
5) Tap Notifications and adjust the settings in there accordingly.
