removing action in wordpress where action has an array with $this - php

Question

I'm trying to simply replace a message that is added by a plugin called 'sensei' from woothemes.
For that my plan was to remove the action that places the message, and then add an action where i copied the normal function and edited to what i wanted it to be.
However the message was never removed and instead my new message is placed on the page next to the default message.
i used this code in functions.php:
add_action( 'sensei_loop_course_inside_before', 'remove_old_course_message', 15 );
add_action( 'sensei_loop_course_inside_before', 'active_no_course_message_output2', 11 );
function remove_old_course_message(){
global $Sensei_Shortcode_User_Courses;
remove_action( 'sensei_loop_course_inside_before', array( 'Sensei_Shortcode_User_Courses', 'sensei_loop_course_inside_before' ), 10);
remove_action( 'sensei_loop_course_inside_before', array( $Sensei_Shortcode_User_Courses, 'sensei_loop_course_inside_before' ), 10);
}
function active_no_course_message_output2(){
?>
<li class="user-active">
<div class="sensei-message info">
This is the message to be shown:
<?php _e( 'You have no active courses.', 'woothemes-sensei' ); ?>
<a href="www.google.com">
<?php _e( 'Start a Course!', 'woothemes-sensei' ); ?>
</a>
</div>
</li>
<?php
}
(all that changed is that i changed the button in the message to link to google instead of another page, this is so the code is a bit more understandable.)
In the plugin file there is a class named 'sensei shortcode-user-courses' and it contains the code:
if( empty( $active_ids ) ){
add_action( 'sensei_loop_course_inside_before', array( $this, 'active_no_course_message_output' ) );
}