Thank you for your reply.
Unfortunately yes, if your contacts are not stored on your SIM card. If you have registered and synced Google account on your phone you will be able to transfer all contacts back.
To unlock you phone please perform the procedure below:
1. Turn off you phone. Remove and replace battery.
2. Press and hold the Volume up, Home and Power buttons at the same time.
3. Release all buttons when you see the Samsung logo.
4. The Android System Recovery screen will be shown.
5. Scroll down to wipe data/factory reset using the Volume down button, then press the Power button to confirm the selection.
6. Scroll to Yes -- delete all user data, then press the Power button.
7. The device will be restored to factory settings.
8. Once finished, scroll to reboot system now, then press the Power button.
Check the picture below to locate buttons
Please note that this procedure require some practice.
Please don't hesitate to ask if you have any difficulties. I will be happy to help with any follow up questions.If you have any difficulties or you need more information please do not rate my answer negative BAD service or POOR service. Reply to me using "Reply to Expert" button and I'll provide you with more help.