Can't load a page with httpwebrequest

I want to take the Flight schedule from the following address:

http://fo-apac.ttinteractive.com/Zenith/FrontOffice/(S(nves1yv4xxoia40cmotixof1))/USBangla/en-GB/BookingEngine/SearchFlights?__cnv=tShqK&json={"BookingPathArguments":null,"OriginDestinations":[{"IsOpen":false,"DataIdOrigin":6337,"DataIdDestination":6707,"DateTime":"2016-04-27T00:00:00.000"}],"TravelerTypes":[{"DataId":1,"TravelerCount":1},{"DataId":2,"TravelerCount":0},{"DataId":3,"TravelerCount":0}],"Currency":{"Code":"BDT"},"PromoCode":null,"DisplayRealAvailability":false,"Visibility":0,"Extended SearchDayCount":3}

If you paste the address to browser address bar and use firebug (or any fiddler), you will see this page sends 3 jquery ajax calls to bring the schedule. The following ajax POST actually fetch the schedule.

http://fo-apac.ttinteractive.com/Zen...ys?__cnv=tShqK

PostData : SaleConditionAccepted=false&ExtendedSearchDayCount=3&DoNotCheckCache=false&AlreadyLoggedIn=false&Tem pDataGuid=nves1yv4xxoia40cmotixof1&CurrencyCode=BDT&FareBasisDataId=&Travelers[0][DataId]=1&Travelers[0][Count]=1&UserSelections[0][SelectedDate]=2016-04-27T00:00:00&UserSelections[0][ReferenceDate]=2016-04-27T00:00:00&UserSelections[0][DataIdOrigin]=6337&UserSelections[0][DataIdDestination]=6707&UserSelections[0][GenericClassDataId]=&UserSelections[0][SelectedSegments]=&JsonPrepareBookingRequest=&PromoCode=

I am sending the request with httpwebrequest, but for unknown reason, I miss the session. I used CookieContainer to keep the cookies. I used the following function to send httprequest:

Code:

---

Public Function GetPostWP(ByVal Url As String, ByVal CkCont As CookieContainer, Optional ByVal PostData As String = "", Optional ByVal refSite As String = "") As String
    Dim pStr As String = ""
    Try
        Dim Http As HttpWebRequest = WebRequest.Create(Url)
        If refSite <> "" Then Http.Referer = refSite
        Http.Headers.Add(HttpRequestHeader.AcceptEncoding, "gzip,deflate")

        Http.CookieContainer = CkCont  'Initial CkCont is Nothing
        Http.KeepAlive = True
        Http.AllowAutoRedirect = True

        'Http.UserAgent = "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2) Gecko/20100115 Firefox/3.6"
        Http.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8"
        Http.UserAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/34.0.1847.137 Safari/537.36"

        If PostData <> "" Then
            Http.Method = "POST"
            Http.ContentLength = PostData.Length
            Http.ContentType = "application/x-www-form-urlencoded"

            Dim PostStream As StreamWriter = New StreamWriter(Http.GetRequestStream())
            PostStream.Write(PostData)
            PostStream.Close()
        End If

        Using WebResponse As HttpWebResponse = Http.GetResponse()
            Dim responseStream As Stream = WebResponse.GetResponseStream()

            If (WebResponse.ContentEncoding.ToLower().Contains("gzip")) Then
                responseStream = New GZipStream(responseStream, CompressionMode.Decompress)
            ElseIf (WebResponse.ContentEncoding.ToLower().Contains("deflate")) Then
                responseStream = New DeflateStream(responseStream, CompressionMode.Decompress)
            End If

            Dim reader As StreamReader = New StreamReader(responseStream, Encoding.Default)
            pStr = reader.ReadToEnd()

            responseStream.Close()
        End Using

        tmpCky = CkCont 'tmpCky is a Public CookieContainer Variable to hold cookies for future use.
        GetPostWP = pStr

    Catch ex As Exception
        GetPostWP = "Error : " & ex.Message
    End Try
End Function

    Dim Cky As New CookieContainer
    Dim Txt as String = GetPostWP(PostAddress, Cky, PostData, RefAdd)

    Cky = tmpCky

---

It is very urgent for my job. Can anyone analyze the page, please?

Thanks