c # Json returning backslash

I'm new to web, I'm trying to return a json but it comes with bars like this:

{\"NomeUsuario\":\"TESTE\",\"TelefoneUsuario\":\"1111111111\"}

How do I make it look like this:

{"NomeUsuario":"TESTE","TelefoneUsuario":"1111111111"}

I have the class person:

[DataContract]
public class Pessoa
{
    [DataMember]
    public string Nome { get; set; }
    [DataMember]
    public string TelefoneUsuario { get; set; }
}

Method

 public string FiltradoPorPessoa(string Nome, string Variavel)
    {
        DataTable Dtconsulta = new DataTable();
        Pessoa retorno = null;

        Sql = " SELECT  NomeUsuario, TelefoneUsuario";
        Sql += " FROM Cadastro.DTUsuario";
        Sql += " WHERE NomeUsuario = '" + Nome.ToUpper() + "' AND SenhaUsuario = '" + GeraHash(Variavel.ToUpper()) + "'";

        DataTable dataTable = new DataTable();
        SqlCommand cmd = new SqlCommand(Sql, conn);
        conn.Open();

        adapter = new SqlDataAdapter(cmd);
        adapter.Fill(dataTable);

        if (dataTable.Rows.Count > 0)
        {
            Pessoa p = new Pessoa();

            DataTableReader DtConsultaReader = dataTable.CreateDataReader();
            while (DtConsultaReader.Read())
            { 
                p.Nome  = DtConsultaReader["NomeUsuario"].ToString();
                p.TelefoneUsuario = DtConsultaReader["TelefoneUsuario"].ToString();
            }
            DtConsultaReader.Close();
            conn.Close();

            var json = new System.Web.Script.Serialization.JavaScriptSerializer().Serialize(p);

            DataContractJsonSerializer ser = new DataContractJsonSerializer(typeof(Pessoa));
            MemoryStream ms = new MemoryStream(Encoding.UTF8.GetBytes(json));
            retorno = (Pessoa)ser.ReadObject(ms);  
        }
        return retorno;     
    }

And a method that returns a datatable, copy that to a datareader, what am I doing wrong, I can not return the string?

  

Can not implicitly convert type 'test15_04.Person' to 'string' in this way {"UserName": "TEST", "UserPhone": "1111111111"}