Check your Apple ID account at https://appleid.apple.com
Open the Apple Support app and view your device coverage
Go to https://checkcoverage.apple.com and enter your device serial number
On iPhone or iPad, go to Settings > General > AppleCare & Warranty
On Mac, go to System Settings > General > About > Coverage
Find the original purchase receipt or AppleCare confirmation email
Contact Apple Support and ask them to verify your coverage
Check your device purchase history in the Apple Store app or Apple account