You restored your device, updated your iOS, deleted and reinstalled the game or switched to a new device and your coins and upgrades are missing.
For iOS: If you enabled iCloud, tap the settings button in the main menu and tap "Restore Backup". If iCloud was never enabled, please contact us at firstname.lastname@example.org
For Android: Tap on the G+ button on the main menu to sign into your Google Play ID. After, tap the settings button and tap "Restore Backup" to view Google Snapshots. From here, choose the progress with the highest percent (%). If you are still not able to restore your progress, please contact us at email@example.com.