Yo don’t properly call the callback function.
If you want to code on oriented object programmation, you have to create your class, and construct function with add_action…
Here more informations about it :
https://wordpress.stackexchange.com/a/48094/9716
or you do something like this (its no POO but its working as well).
add_action( 'woocommerce_subscription_status_active', 'add_subscription_course_access' ) );
function add_subscription_course_access( $order )
{
$products = $order->get_items();
$customer_id = $order->get_customer_id();
$courses_id = get_field('user-programs', 'user_'. $customer_id);
$courses_id = str_replace("[","",$courses_id);
$courses_id = str_replace("]","",$courses_id);
$courses_id = explode(",",$courses_id);
foreach ( $courses_id as $course_id ) {
ld_update_course_access( $customer_id, $course_id );
}
}