Excluding posts not working

Have a look at https://codex.wordpress.org/Class_Reference/WP_Query, and maybe try passing your args in an array.
Above page lists this exact example, which should work:

// This WILL work
$exclude_ids = array( 1, 2, 3 );
$query = new WP_Query( array( 'post__not_in' => $exclude_ids ) );