Billing question

The offer is for Apple TV+, not Apple TV. Apple TV+ is a very specific service.

You need a valid payment method to start a subscription, but a credit card is not strictly needed, however that is the most convenient option. Subscriptions require a payment method that can be billed automatically and periodically without repeated approval. To start a subscription with just account balance, you will need to add the amount of one billing cycle (plus taxes, if applicable).

Payment methods that you can use with your Apple ID - Apple Support

Change, add, or remove Apple ID payment methods - Apple Support

Please contact AppleCare to ask that question. However it sounds like you did not redeem your offer, did you use the advice in Apple TV+ One Year Offer - Apple