/**
 * Hide shipping rates when free shipping is available
 */

add_filter('woocommerce_package_rates', 'cc_hide_shipping_when_free_is_available', 100);

function cc_hide_shipping_when_free_is_available($rates) {

  $free = array();
  foreach ($rates as $rate_id => $rate) {
    if ('free_shipping' === $rate->method_id) {
      $free[$rate_id] = $rate;
      break;
    }
  }

  return ! empty($free) ? $free : $rates;

}