This will hide the single product page the proper WordPress way by making the product not public.

Pop this into your functions.php file.

add_filter( 'woocommerce_register_post_type_product','hide_product_page',12,1);
function hide_product_page($args){
    $args["publicly_queryable"]=false;
    $args["public"]=false;
    return $args;
}

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