Chart item named '0' already exists in 'SeriesCollection'

I am developing a fairly simple code that allows me to query the database to retrieve values ​​from two columns. My problem is that when I try to use two x through the DataBindTable the following error appears: A graph element named "0" Already exists in "SeriesCollection".

I was grateful for the help.

Why is this error occurring?

Here is my code:

        string cs1 = ConfigurationManager.ConnectionStrings["CS"].ConnectionString;

        using (SqlConnection con1 = new SqlConnection(cs1))
        {
            SqlCommand cmd1 = new SqlCommand(" USE [DB_SACC] SELECT  [Consumo_Medio_Real],[Tipo_de_Fatura]   FROM [dbo].[t_faturas]", con1);

            con1.Open();

            SqlDataReader rdr1 = cmd1.ExecuteReader();

            var dt1 = new System.Data.DataTable();

            dt1.Load(rdr1);

            var enumerableTable1 = (dt1 as System.ComponentModel.IListSource).GetList();


            Chart1.DataBindTable(enumerableTable1, "Tipo_de_Fatura");




            string cs = ConfigurationManager.ConnectionStrings["CS"].ConnectionString;

            using (SqlConnection con = new SqlConnection(cs))
            {
                SqlCommand cmd = new SqlCommand("USE [DB_SACC] SELECT [Consumo_Mes_Anterior], [N_Leituras] FROM [dbo].[t_leituras]", con);

                con.Open();

                SqlDataReader rdr = cmd.ExecuteReader();

                var dt = new System.Data.DataTable();

                dt.Load(rdr);

                var enumerableTable = (dt as System.ComponentModel.IListSource).GetList();

                Chart1.DataBindTable(enumerableTable, "N_Leituras");


            }

        }

      

        
        
        
      

    

Here's the html code of the chart:

    <asp:Chart ID="Chart1" runat="server" DataSourceID="SqlDataSource1" Height="293px" OnLoad="Chart1_Load16" Width="801px">
                          <Series>
                              <asp:Series Name="Series1">
                              </asp:Series>
                          </Series>
                          <ChartAreas>
                              <asp:ChartArea Name="ChartArea1">
                              </asp:ChartArea>
                          </ChartAreas>
                      </asp:Chart>