Wordpress重写已有页面的网址

Hi I'm having an issue while rewriting a url like this "news/category_name_here/page_num_here" when I already have a page with the link of "news" it seems to be always considering the first parameter as something else and not the get_query_var I gave it, e.g. category_name_here wouldn't be defined in the call to get_query_var()

Here is my code I was explaining:

function prefix_register_query_var( $vars ) {
    $vars[] = 'cat';
    $vars[] = 'pagenum';

    return $vars;
}
add_filter( 'query_vars', 'prefix_register_query_var' );

function custom_rewrite_rule() {
    add_rewrite_rule('^news/([^/]*)/([^/]*)/?','index.php?page_id=51&cat=$matches[1]&pagenum=$matches[2]','top');
    flush_rewrite_rules();
}
add_action('init', 'custom_rewrite_rule', 10, 0);

Thanks in advance.

Seem to have solved it. The issue was that the term "cat" was protected.