Hide shipping methods if freeshipping/flatrate exists.

function.php

add_filter('woocommerce_package_rates', 'xa_hide_shipping_methods_if_free_flaterate_exist', 10, 2);
if(!function_exists('xa_hide_shipping_methods_if_free_flaterate_exist')){
    function xa_hide_shipping_methods_if_free_flaterate_exist( $available_shipping_methods, $package ){

        $hide_if_shpping_method_exist = array('free_shipping','flat_rate'); //If the shipping methods given here is exists.
        $method_to_hide = array('wf_australia_post'); //Hide all the shipping method provided here.

        $do_hide = false;
        foreach ($hide_if_shpping_method_exist as $method) {
            foreach ($available_shipping_methods as $shipping_method => $value) {
                if( strpos( $shipping_method, $method ) !== false ) {
                    $do_hide=true;
                    break 2;
                }
            }
        }

        if( $do_hide ){
            foreach ($method_to_hide as $method) {
                xa_hide_the_shipping_method( $method, $available_shipping_methods );
            }
        }
        return $available_shipping_methods;
    }
}

if(!function_exists('xa_hide_the_shipping_method')){
    function xa_hide_the_shipping_method($method, &$available_shipping_methods){
        foreach ($available_shipping_methods as $shipping_method => $value) {
            if( strpos( $shipping_method, $method ) !== false ) {
                unset($available_shipping_methods[$shipping_method]);
            }
        }
        return $available_shipping_methods;
    }
}