Open the upgrade screen and tap Restore Purchases while connected to the internet. Make sure you are signed in with the same store account that made the purchase.
No. It is a single one-time payment. Nothing renews and nothing is charged again.
Up to 3 tracked items, for as long as you like — with reminders, categories, search, statistics and backup all included. There is no time limit and no account. If you need more than 3 items, the one-time purchase removes the limit.
Yes: Settings → Backup saves a file, and Restore on the new phone reads it back. There is no cloud sync — your data never leaves your device unless you move the file yourself.
Unfortunately it is gone. Nothing is stored on any server, so there is no copy to recover. Use Backup regularly if the list matters to you.
Refunds are handled by the store, not by us: reportaproblem.apple.com for iOS, or the Google Play order history for Android.
Write to snur.adibelli@gmail.com. Bug reports that say what you did, what you expected and what happened instead get fixed fastest.