To get rid of a persistent pop-up notification, here are the steps to follow:

1. Disable unnecessary notifications in Settings or System Preferences.

2. Check to make sure that all background processes are closed.

3. Review all installed apps to determine which one is sending the popup notification.

4. Uninstall or disable the app that is sending the popup notification.

5. Malware Check: Check for malware, spyware, and other malicious programs.