Disable keepalive in webservice class

Hello, How can I turn off keep alive in the following class? I'm a newb with c# and with web services and would appreciate the help as I sometimes get the following error:

The underlying connection was closed: A connection that was expected to be kept alive was closed by the server.

on this line of code:
 this.RawXml = ws.GetQuote(this.Symbol);

In this code block:
private void GetQuote()
    {
        using (StockQuoteService.StockQuote ws = new StockQuoteService.StockQuote())
        {
            this.RawXml = ws.GetQuote(this.Symbol);
        }

        XmlDocument doc = new XmlDocument();
        doc.InnerXml = this.RawXml;
        foreach (XmlNode node in doc.FirstChild.FirstChild.ChildNodes)
        {
            this.Parameters.Add(node.Name, node.InnerText);
        }
    }




using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Xml;
using System.Collections.Specialized;

/// <summary>
/// Summary description for StockQuote
/// </summary>
public class StockQuote
{
    private string _symbol = string.Empty;
    public string Symbol
    {
        get { return _symbol; }
        set { _symbol = value; }
    }

    private string _raw_xml = string.Empty;
    public string RawXml
    {
        get { return _raw_xml; }
        set { _raw_xml = value; }
    }

    private NameValueCollection _parameters = new NameValueCollection();
    public NameValueCollection Parameters
    {
        get { return _parameters; }
        set { _parameters = value; }
    }

    public string Last
    {
        get { return GetParameter("Last"); }
    }

    public DateTime QuoteDateTime
    {
        get
        {
            DateTime dVal = DateTime.Now;
            DateTime.TryParse(GetParameter("Date") + " " + GetParameter("Time"), out dVal);
            return dVal;
        }
    }

    public string Change
    {
        get { return GetParameter("Change"); }
    }


      public StockQuote()
      {
            //
            // TODO: Add constructor logic here
            //
      }

    public StockQuote(string symbol)
    {
        this.Symbol = symbol;
        GetQuote();
    }

    private void GetQuote()
    {
        using (StockQuoteService.StockQuote ws = new StockQuoteService.StockQuote())
        {
            this.RawXml = ws.GetQuote(this.Symbol);
        }

        XmlDocument doc = new XmlDocument();
        doc.InnerXml = this.RawXml;
        foreach (XmlNode node in doc.FirstChild.FirstChild.ChildNodes)
        {
            this.Parameters.Add(node.Name, node.InnerText);
        }
    }

    private string GetParameter(string key)
    {
        if (this.Parameters[key] == null)
        {
            throw new Exception(string.Format("I could not find the key ({0}) you are looking for", key));
        }
        return this.Parameters[key];
    }

}