public List<Order> FindOrder(string custemail, string orderstatus)
{
   var findorder = from r in order.Orders 
                   where (r.CustEmail  == custemail && r.OrderStatus == orderstatus ) 
                   select r;
   return findorder.ToList();
}

public pgShopCart()
{    
    var obj = App.Current as App;
    custemail = obj.custEMAIL;
    string orderstatus = "Pending";
    proxy.FindOrderCompleted += new EventHandler<FindOrderCompletedEventArgs>(proxy_FindOrderCompleted);
    proxy.FindOrderAsync(custemail, orderstatus);
}

void proxy_FindOrderCompleted(object sender, FindOrderCompletedEventArgs e)
{
    ListBox1.ItemsSource = e.Result;
}

void proxy_FindOrderCompleted(object sender, FindOrderCompletedEventArgs e)
{
    ListBox1.ItemsSource = e.Result;
    ObservableCollection<Order> Orders = this.ListBox1.ItemsSource as ObservableCollection<Order>;

    foreach (Order order in Orders)
    {
        orderid = order.OrderID;
    } 
}

public void UpdateOrderStatus(int orderid, string orderstatus, string paymentdate)
{
    Order data = order.Orders.Single(p => p.OrderID == orderid);
    data.OrderStatus = orderstatus;
    order.SubmitChanges();
}

private void btnPay_Click(object sender, RoutedEventArgs e)
{
    proxy.UpdateOrderStatusCompleted += new EventHandler<UpdateOrderStatusCompletedEventArgs>(proxy_UpdateOrderStatusCompleted);
    proxy.UpdateOrderStatusAsync(orderid, orderstatus);
}