Removing special character from the string does not work. W#

I have this string :

EM RECUPERA�?�?O

This string comes in a XML and I use the following code to handle this:

byte[] bytes = Encoding.Default.GetBytes(xmlRetorno);
xmlRetorno = Encoding.UTF8.GetString(bytes);

But it is not working. It's still the same.

So I return the XML:

public string EnviarXmlSoap(string methodName, string body, string url)
    {
        WebRequest webRequest = WebRequest.Create(url);
        HttpWebRequest httpRequest = (HttpWebRequest)webRequest;
        httpRequest.Method = "POST";
        httpRequest.ContentType = "text/xml; charset=utf-8";
        httpRequest.Headers.Add("SOAPAction: http://tempuri.org/" + methodName);
        httpRequest.ProtocolVersion = HttpVersion.Version11;
        httpRequest.Credentials = CredentialCache.DefaultCredentials;
        Stream requestStream = httpRequest.GetRequestStream();
        //Create Stream and Complete Request             
        StreamWriter streamWriter = new StreamWriter(requestStream, Encoding.UTF8);

        StringBuilder soapRequest = new StringBuilder("<soapenv:Envelope xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\"");
        soapRequest.Append(" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" ");
        soapRequest.Append("xmlns:soapenv=\"http://schemas.xmlsoap.org/soap/envelope/\" xmlns:urn=\"urn:"+methodName+"\" xmlns:soapenc=\"http://schemas.xmlsoap.org/soap/encoding/\"> <soapenv:Header/> <soapenv:Body>");
        soapRequest.Append(body);
        soapRequest.Append("</soapenv:Body></soapenv:Envelope>");

        streamWriter.Write(soapRequest.ToString());
        streamWriter.Close();

        string xml = soapRequest.ToString();

        //Get the Response    
        HttpWebResponse wr = (HttpWebResponse)httpRequest.GetResponse();
        StreamReader srd = new StreamReader(wr.GetResponseStream());
        string resulXmlFromWebService = srd.ReadToEnd();
        return resulXmlFromWebService;
    }