If you were already subscribed to Apple TV+ then you are not eligible for another free offer.
If you are a first time user and received the 7 day free trial instead of the 3 month free trial, then you'll need to contact Apple Support directly to get the free offer correctly applied now. Link-> Apple Support
If you simply want to cancel the subscription now that the free offer has ended, then follow the steps here: link-> If you want to cancel a subscription from Apple - Apple Support
You can contact Apple Support to request a refund once its cancelled: link-> Request a Refund for Cancelled Subscription - Apple Support