Write to hello@nanuli.app and a person will answer. Include the device you are using and what happened; if the app misbehaved during a recording, say which story and which scene.
In the app, on the device you made them on. There is no account and no server: the app makes no network calls of its own, so nothing is uploaded and nothing can be recovered by us. Keep your device backup on if the recordings matter to you.
Settings, then "Delete all recordings". They are gone immediately and for good. Deleting the app removes them too.
Settings, then "Manage subscription" — it opens Apple's subscription page. You can also go to Settings on the device, tap your name, then Subscriptions. Cancelling stops the next renewal; the period you paid for runs to the end.
Stories you have already recorded keep playing. Stories you have not started lock until you subscribe again.
The recording never leaves the device, so nobody else can hear it — not us, not Apple. If you would rather record alone, turn off "Read together" in Settings and the story goes back to one voice.