parse and extract xml data and reply using a webservice in c#.net

<COMMAND>
               <TYPE>PAYMENT</TYPE>
               <COMPANYNAME>gemeya</COMPANYNAME>
               <CUSTOMERREFERENCEID>910573404</CUSTOMERREFERENCEID>
               <MSISDN>msisdn</MSISDN>
               <AMOUNT>45150.00</AMOUNT>
               <TXNID></TXNID>
               <STATUS></STATUS>
   </COMMAND>

01.ALTER PROCEDURE [dbo].[GetCheckoutInfoTest]
02.@Refcode nvarchar(100)
03.,@Amount nvarchar(100)
04.AS
05. BEGIN
06.    DECLARE @Price AS float
07.    DECLARE @RefId AS int
08.    DECLARE @TXTNID AS NVARCHAR(50)
09.    DECLARE @companyname AS NVARCHAR(50)
10.      
11.    SET @Price=(SELECT Amount FROM Checkout  Where Refcode=@Refcode)
12.    SET @RefId=(SELECT Refcode FROM Checkout WHERE Refcode=@Refcode)
13.    SET @TXTNID='GBPHANDLER'
14.    SET @companyname='Gemeya'
15.    if exists(SELECT Amount,Refcode FROM Checkout  Where Refcode=@Refcode)
16.      begin
17.        if(@Amount=@Price and @RefId=@Refcode)
18.        begin
19.          PRINT N'Your transaction successfull. Txn ID:'+ @TXTNID +', reference: '+
20.          @Refcode +', amount :'+ @Amount +' Tsh, Company: '+ @companyname;
21.         return 1
22.        end
23.      end
24.      else
25.      begin
26.       PRINT N'Your transaction Failed';
27.        return 0
28.      end
29. END

01.public class Service : System.Web.Services.WebService
02.{
03.    public int Amount { get; set; }
04.    public int Refcode { get; set; }
05.    public int companycode { get; set; }
06.    public bool IsUsed { get; set; }
07.    public string PhoneNo { get; set; }
08.   #region method constructor
09.    public Service()
10.    {
11.       //Uncomment the following line if using designed components 
12.        //InitializeComponent(); 
13.    }
14.    #endregion
15.    [WebMethod]
16.    public string COMMAND(string xml)
17.    {
18.        #region Load received xml and parse the values
19.        XmlDocument xdoc = new XmlDocument();
20.        xdoc.LoadXml(xml + Environment.NewLine);
21.        string TYPE = xdoc["COMMAND"].ChildNodes[0].InnerText;
22.        string COMPANYNAME = xdoc["COMMAND"].ChildNodes[1].InnerText;
23.        string CUSTOMERREFERENCEID = xdoc["COMMAND"].ChildNodes[2].InnerText;
24.        string MSISDN = xdoc["COMMAND"].ChildNodes[3].InnerText;
25.        string AMOUNT = xdoc["COMMAND"].ChildNodes[4].InnerText;
26.        string TXNID = xdoc["COMMAND"].ChildNodes[5].InnerText;
27.        string STATUS = xdoc["COMMAND"].ChildNodes[6].InnerText;
28.        #endregion
29.       string ERRORCODE = string.Empty;
30.        string RESULT = string.Empty;
31.        string FLAG = string.Empty;
32.        string CONTENT = string.Empty;
33.        //process your code with received information and assign the values of ERRORCODE,RESULT,FLAG,CONTENT
34.        StringBuilder sb = new StringBuilder();
35.        DataSet ds = SqlHelper.ExecuteDataset(SqlHelper.GetConnection(), "[GetCheckoutInfoTest]",  
36.        CUSTOMERREFERENCEID,AMOUNT);
37.        if (ds.Tables[0].Rows.Count > 0)
38.        {
39.            //assign the values of ERRORCODE,RESULT,FLAG,CONTENT when condition is true
40.            RESULT = "TS";
41.        }
42.        else
43.        {
44.            //assign the values of ERRORCODE,RESULT,FLAG,CONTENT when condition is false
45.            RESULT = "TF";
46.        }
47. 
48. 
49.        #region write the response xml
50.        XmlWriter writer = XmlWriter.Create(sb);
51. 
52. 
53.            writer.WriteStartDocument();
54.            writer.WriteStartElement("COMMAND");
55.            writer.WriteStartElement("TYPE");
56.            writer.WriteValue(TYPE);
57.            writer.WriteEndElement();
58.            writer.WriteStartElement("TXNID");
59.            writer.WriteValue(TXNID);
60.            writer.WriteEndElement();
61.            writer.WriteStartElement("REFID");
62.            writer.WriteValue(CUSTOMERREFERENCEID);
63.            writer.WriteEndElement();
64.            writer.WriteStartElement("ERRORCODE");
65.            writer.WriteValue(ERRORCODE);
66.            writer.WriteEndElement();
67.            writer.WriteStartElement("FLAG");
68.            writer.WriteValue(FLAG);
69.            writer.WriteEndElement();
70.            writer.WriteStartElement("MSISDN");
71.            writer.WriteValue(MSISDN);
72.            writer.WriteEndElement();
73.            writer.WriteStartElement("CONTENT");
74.            writer.WriteValue(CONTENT);
75.            writer.WriteEndElement();
76.            writer.WriteStartElement("COMPANYCODE");
77.            writer.WriteValue(COMPANYNAME);
78.            writer.WriteEndElement();
79.            writer.WriteStartElement("AMOUNT");
80.            writer.WriteValue(AMOUNT);
81.            writer.WriteEndElement();
82.            writer.WriteEndElement();
83.            writer.WriteEndDocument();
84.            writer.Flush();
85.            #endregion
86.     return sb.ToString();
87.      }