I was also a little confused by this, but one situation where you might continue to receive notifications is if you fail to acknowledge the notification by returning a 200 status back to Twitch. In that situation, Twitch will repeat the notification several times, with an increasing backoff timer, before giving up.
If you properly handle notification acknowledgement, and are still getting continuous notifications as it seems like you are from the way you describe it, then something isn’t working as intended.