How Do I Invoke Or Call Soap Xml Web Service In Asp.Net

public string  SoapPatientMedication()
    {   string resultXml;
        WebRequest wbrqst = WebRequest.Create("http://preproduction.newcropaccounts.com/v7/WebServices/Patient.asmx");
        HttpWebRequest httpreq = (HttpWebRequest)wbrqst;
        httpreq.Method = "POST";
        httpreq.ContentType = "text/xml charset=utf-8";
        httpreq.Headers.Add("SOAPAction","https://secure.newcropaccounts.com/V7/webservices/GetPatientFullMedicationHistory");
        httpreq.ProtocolVersion = HttpVersion.Version11;
        httpreq.Credentials = CredentialCache.DefaultCredentials;
        Stream requestStream = httpreq.GetRequestStream();
        StreamWriter streamWriter = new StreamWriter(requestStream, Encoding.ASCII);
        StringBuilder sb = new StringBuilder();
        sb.Append("<soap:Envelope xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance' xmlns:xsd='http://www.w3.org/2001/XMLSchema' xmlns:soap='http://schemas.xmlsoap.org/soap/envelope/'>");
        sb.Append("<soap:Body>");
        sb.Append("<GetPatientFullMedicationHistory xmlns='https://secure.newcropaccounts.com/V7/webservices'>");
        sb.Append("<credentials>");
        sb.Append("<PartnerName>demo</PartnerName>");
        sb.Append("<Name>demo</Name>");
        sb.Append("<Password>demo</Password>");
        sb.Append("</credentials>");
        sb.Append("<accountRequest>");
        sb.Append("<AccountId>demo</AccountId>");
        sb.Append("<SiteId>demo</SiteId>");
        sb.Append("</accountRequest>");
        sb.Append("<patientRequest>");
        sb.Append("<PatientId>16</PatientId>");
        sb.Append("</patientRequest>");
        sb.Append("<prescriptionHistoryRequest>");
        sb.Append(" <StartHistory>2004-01-01T00:00:00.000</StartHistory>");
        sb.Append("<EndHistory>2012-01-01T00:00:00.000</EndHistory>");
        sb.Append("<PrescriptionStatus>C</PrescriptionStatus>");
        sb.Append("<PrescriptionSubStatus>%</PrescriptionSubStatus>");
        sb.Append("<PrescriptionArchiveStatus>N</PrescriptionArchiveStatus>");
        sb.Append("</prescriptionHistoryRequest>");
        sb.Append("<patientInformationRequester>");
        sb.Append("<UserType>demo</UserType>");
        sb.Append("<UserId>demo</UserId>");
        sb.Append("</patientInformationRequester>");
        sb.Append("</GetPatientFullMedicationHistory>");
        sb.Append("</soap:Body>");
        sb.Append("</soap:Envelope>");

        streamWriter.Write(sb.ToString());
        streamWriter.Close();
        HttpWebResponse wr = (HttpWebResponse)httpreq.GetResponse();
        StreamReader srd = new StreamReader(wr.GetResponseStream());
        resultXml = srd.ReadToEnd();
        return resultXml;

    }