Payment PlugIn NotificationHandler

Hi, I developed a payment plugin that redirect the customer to external site for credit cart payment.
Everything working fine but I am not able to manage in right way the NotificationHandler in PaymentController
in case of right result of payment from external site.
RedirectToRoute does not work as follow:

      _orderService.UpdateOrder(order);

            if (esito == "OK" && responseCode == "000")
            {
                _orderProcessingService.MarkOrderAsPaid(order);
                RedirectToRoute("CheckoutCompleted");

            }
            else
            {
                RedirectToAction("Index", "Home", new { area = "" });
            }
        }

What I have to do to redirect customer into the right page ..if possible another confirmation page.

Second question is the idea of redirect the customer in case of payment failure in the shopping cart page: mainly I do not want to delete the cart. Any suggestion?

I am more or less close to the creation of this plugin but I miss something to complete..

Thanks in advance...

Massimo

No body should help me?

Thanks