Gaman needs Screen Time permission and at least one app selected, and blocking has to be on. Open Gaman: the status card says Blocked when it is running. If it says Off, tap Start blocking.
Answering closes the wall and posts a notification. iOS does not let an app extension open its own app, so tapping that notification is the way back into Gaman. If no notification arrives, turn notifications on — Gaman shows a card for this on its main screen.
Open Gaman and tap Stop blocking. With Strict mode on there are no passes, so turning blocking off is the only way out — that is the point of it.
On your iPhone: Settings → your name → Subscriptions → Gaman. Cancelling there stops future charges; Apple handles all billing.
Tap Restore purchases on the subscription screen while signed in with the same Apple Account.
Everything Gaman records is on your device. Deleting the app deletes all of it. There is nothing on a server to delete.