我应该在哪里取消WooCommerce运费？

I need to unset a WooCommerce shipping rate, and have come up with this function too loop through the products in the order and add up their weight. I need to unset the UPS option if the weight is greater than 50 lbs:

add_filter( 'coocommerce_package_rates', 'hide_ups_over_50', 10, 2 );

function hide_ups_over_50( $rates, $package ) {
    $totalWt = 0;
    $items = $package[contents];
    foreach ($items as $item) {
        $quantities[] = $item[quantity];
        if ( strlen( $item[variation_id] ) ) {
            $prodIDs[] = $item[variation_id];
        } else {
            $prodIDs[] = $item[product_id];
        }
        $productMeta = get_post_meta($item[product_id]);
        $itemWt = $productMeta['_weight'][0];
        $totalWt = $totalWt + ($itemWt * $item['quantity'] );
    }
    if( $totalWt > 50 ) {
        unset( $rates['ups:03'] );
    }
    // Return what's left of the $rates array
    return $rates;
}

I have tried putting it in the functions.php file of my theme, and also just using the calculations and the unset() call inside of a plugin I wrote that calculates freight shipping costs. Either way, it doesn't unset the ups:03 shipping rate. I'd rather not edit the UPS plugin if it can be avoided. Where should this function be called?