App claims it's open, refuses to close
You can remove most apps when they are not running, so move the app to the trash and then log out of your Mac from the Apple menu - Log out...

When you log back in, the app won’t start since it’s in the Trash and then you can empty it.

As long as it’s a normal app and not one that installed helpers, start at boot, or malware this works for all basic apps. Non-basic apps or ones that run hidden helpers like most Adobe products, Zoom, backup and remote control software need to be uninstalled or deactivated based on how they were implemented. 

Live Chat may need an uninstall...


  ... start automatically when you turn on your computer, so you never miss a chat.


If you struggle, the steps to isolate malware and persistent apps might need a follow on question based on how your mac is set up, and the specific of the exact app you have.