WooCommerce Cancelled orders sent to client also

cancelled_order_add_customer_email.php

<?php

add_filter( 'woocommerce_email_recipient_cancelled_order', 'cancelled_order_add_customer_email', 10, 2 );
function cancelled_order_add_customer_email( $recipient, $order ) {
	if ( $order ) {
		return $recipient . ',' . ( version_compare( WC_VERSION, '3.0', '>=' ) ? $order->get_billing_email() : $order->billing_email );
	} else {
		return $recipient;
	}
}