Google Voice, in C#: how to delete a sms or how to mark it as read?

Question

With C#, how do I delete a sms on Google Voice? Alternatively, how do I mark a sms as read? I'd rather delete it but marking it would be ok too.

As far as marking it as read I tried this

    public String markAsRead(string _authToken, string _msgID, string rnrSEE)
    {
        String smsdata = HttpUtility.UrlEncode("auth", Encoding.UTF8) + "="
                + HttpUtility.UrlEncode(_authToken, Encoding.UTF8);
        smsdata += "&" + HttpUtility.UrlEncode("messages", Encoding.UTF8) + "="
                + HttpUtility.UrlEncode(_msgID, Encoding.UTF8);
        smsdata += "&" + HttpUtility.UrlEncode("read", Encoding.UTF8) + "="
                + HttpUtility.UrlEncode("1", Encoding.UTF8);
        smsdata += "&" + HttpUtility.UrlEncode("_rnr_se", Encoding.UTF8) + "="
                + HttpUtility.UrlEncode(rnrSEE, Encoding.UTF8);

        //POST /voice/inbox/mark/ messages=[message id]&read=1&_rnr_se=[pull from page]

        return this.makeRequest("https://www.google.com/voice/inbox/mark/", smsdata);
    }

    public String makeRequest(String url, String data)
    {
        string result = null;

        WebResponse response = null;
        StreamReader reader = null;
        try
        {
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
            request.Method = "POST";
            request.ContentType = "application/x-www-form-urlencoded";
            request.ContentLength = data.Length;

            using (Stream writeStream = request.GetRequestStream())
            {
                UTF8Encoding encoding = new UTF8Encoding();
                byte[] bytes = encoding.GetBytes(data);
                writeStream.Write(bytes, 0, bytes.Length);
            }

            response = request.GetResponse();
            reader = new StreamReader(response.GetResponseStream(), Encoding.UTF8);
            result = reader.ReadToEnd();

        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
            throw new IOException(ex.Message);
        }
        finally
        {
            if (reader != null)
                reader.Close();
            if (response != null)
                response.Close();
        }

        if (result.Equals(""))
        {
            throw new IOException("No Response Data Received.");
        }

        return result;
    }

                                            markAsRead(authTokenAccount1, msgFromAccount1, voiceConnectionAccount1.rnrSEE);

but it doesn't work just returns html for the login screen

This site http://posttopic.com/topic/google-voice-add-on-development says to mark a message as read u have to post this data to

messages=[message id]&read=1&_rnr_se=[pull from page]

to this site

/voice/inbox/mark/

could someone tell me what im doing wrong?

Thanks!