Letters you will never send.
Email cewmalainine@gmail.com. Include your device model and iOS version; there is no account, so we cannot look you up by name.
Where are my letters stored? Only on your phone. Nothing you write is uploaded, and there is no account. If you delete the app, the letters go with it, so export anything you want to keep first.
Can anyone read them? No. Letters never leave your device. When you share a letter as an image, you choose where it goes and the image carries no name.
How do I cancel? Subscriptions are managed by Apple. Open Settings → your name → Subscriptions → Unsent.
How do I delete my data? Delete the app. There is nothing stored off your phone.