Why does WordPress keep showing me error messages?

I’m trying to hide error messages on a WordPress installation on a shared hosting. I added the following code to my config.

ini_set('display_errors','Off');
ini_set('error_reporting', E_ALL );
define('WP_DEBUG', false);
define('WP_DEBUG_DISPLAY', false);

This is pretty much what I find in any article regarding this topic. However, it doesn’t work. I keep getting error messages. What could be the reason it isn’t working for me?