To avoid depleting your mobile data plan, you can choose to disable the automatic download of photos and videos in Viber when your smartphone is connected to cellular data. This will pause downloads of any photos and videos shared via Viber until you're once again connected to a WiFi network.
Disable Media Auto Download in Viber
Launch the Viber app and tap on the Menu key > Settings:
Tap on Media:
Clear the Auto download photos and Auto download videos checkboxes: