Number Of Products Sold

I use this snipet to display Number Of Products Sold:

<?php
add_action( 'woocommerce_single_product_summary', 'wc_product_sold_count', 11 );
function wc_product_sold_count() {
global $product;
$units_sold = get_post_meta( $product->id, 'total_sales', true );
echo '<p>' . sprintf( __( 'Units Sold: %s', 'woocommerce' ), $units_sold ) . '</p>';
}
?>

But when the order being canceled, it doesn’t change anything. It should show the number before the order was placed. Ex:

Before placing order: 10
after placing order : 15
Cancel order : 15 (it’s still there) but I want it’s 10

Anyone can help me?

https://wordpress.org/plugins/woocommerce/