Send a Custom Email on Order Status Change

<?php

  
// Targets custom order status "refused"
// Uses 'woocommerce_order_status_' hook
  
add_action( 'woocommerce_order_status_refused', 'bbloomer_status_custom_notification', 20, 2 );
  
function bbloomer_status_custom_notification( $order_id, $order ) {
      
    $heading = 'Order Refused';
    $subject = 'Order Refused';
  
    // Get WooCommerce email objects
    $mailer = WC()->mailer()->get_emails();
  
    // Use one of the active emails e.g. "Customer_Completed_Order"
    // Wont work if you choose an object that is not active
    // Assign heading & subject to chosen object
    $mailer['WC_Email_Customer_Completed_Order']->heading = $heading;
    $mailer['WC_Email_Customer_Completed_Order']->settings['heading'] = $heading;
    $mailer['WC_Email_Customer_Completed_Order']->subject = $subject;
    $mailer['WC_Email_Customer_Completed_Order']->settings['subject'] = $subject;
  
    // Send the email with custom heading & subject
    $mailer['WC_Email_Customer_Completed_Order']->trigger( $order_id );
  
    // To add email content use https://businessbloomer.com/woocommerce-add-extra-content-order-email/
    // You have to use the email ID chosen above and also that $order->get_status() == "refused"
      
}