Send an email notification when order status change from pending to cancelled in WooCommerce

functions.php

add_action('woocommerce_order_status_pending_to_cancelled', 'cancelled_send_an_email_notification', 10, 2 );
function cancelled_send_an_email_notification( $order_id, $order ){
    // Getting all WC_emails objects
    $email_notifications = WC()->mailer()->get_emails();

    // Sending the email
    $email_notifications['WC_Email_Cancelled_Order']->trigger( $order_id );
}

https://stackoverflow.com/questions/45732404/send-an-email-notification-when-order-status-change-from-pending-to-cancelled