You probably created a new account and activated a new subscription on this account somehow when setting up the Peackock app on your Firestick.
Which one do you want to keep?
You can go into your Amazon account and cancel the Peackock subscription from there. Then log out on the app, and log in with the Apple ID and password that holds your other subscription if that is what you want.
Or, cancel the Apple based subscription, log out form your Apple ID, and log in with your original Amazon Account that holds the other subscription.
click here ➜ If you want to cancel a subscription from Apple - Apple Support