C# 如何在千位添加逗号作为双精度

如何在双精度中添加逗号 这是我拥有的代码，但它没有给我想要的东西。 任何帮助不胜感激，谢谢

class invoice
{
    private static int invoiceNumber = 0;
    private String customerName;
    private double total = 0;
    public invoice(String name, invoiceLineItem[] item)
    {
        invoiceNumber = invoiceNumber + 1;
        customerName = name;
        Console.WriteLine("Invoice Number :" + invoiceNumber);
        Console.WriteLine(customerName);
        Console.WriteLine("Product Number'tDescription't    Quantity't   Unit Price'tExtended Price'n");
        for (int i = 0; i < item.Length; i++)
        {
            item[i].displayItem();
            total = total + item[i].getExtendedPrice();
        }
        Console.WriteLine("-------------------------------------------------------------------------");
        String.Format("{0:N} Invoice Total:                                          " + total);// here is where i want to add a comma to the double total 
        Console.WriteLine("");
    }