Write to support@app-cal.fit. You will hear back within two or three days.
You can delete your account from inside the app: Profile, then Delete account. It removes everything held on the server and everything held on the device. If you cannot reach the app, write to the address above from the email address you signed up with.
Subscriptions are handled by your Apple account. Cancelling and refunds happen in Settings, your name, Subscriptions, not through us.