Apple TV

Did you follow these instructions ?

Offer must be claimed within 90 days from when you activated the new device 

Open the Apple TV app. Make sure your device is running the latest version of iOS, iPadOS, tvOS, or macOS.

The offer should be presented immediately after launching the app. If not, go to the Apple TV+ channel page where you’ll see the offer.

Tap Enjoy 1 Year Free.

Apple TV + Offer

https://support.apple.com/en-us/HT210573

Was this a recent purchase? If bought previously then the offer would only be valid for 3 months after device activation.

Are you a new subscriber? If you had already been subscribed then you would not be entitled to the free offer.

If you have verified and are still having issues then best to contact Apple support.