protected void Page_Load(object sender, EventArgs e)
        {
            GridView1.DataSource = ws.GetStatusFromBill("Guardada");
            GridView1.DataBind();

            GridView2.DataSource = ws.GetStatusFromBill("Anulada");
            GridView2.DataBind();

            GridView3.DataSource = ws.GetStatusFromBill("Emitida");
            GridView3.DataBind();
        }