When the Viber messages or any other files get erased from an Android, they still exist on the device until & unless they are not overwritten by the new stuff. In such a situation, you can try any third-party program such as Android Data Recovery to recover deleted Viber messages on Android easily.
To know more: https://recover-androiddata.com/recover-deleted-viber-messages-on-android/

If you have lost any of your important contacts from your Android device, then let me tell you that they are not actually deleted. Those contacts are still present on your phone but in a hidden manner. In such a situation, you are required to use the best and most reliable Android Data recovery software. This program will not only help you to retrieve your lost contacts but also restores pictures, video clips, chats, notes, music, documents, etc.
So, without any delay just download and install this program from the below-given link and get back all your files including contacts. Good luck!!!
https://recover-androiddata.com/download-android-recover