FileStream没有为下一循环创建新文件，请覆盖现有文件

如何解决FileStream没有为下一循环创建新文件，请覆盖现有文件

我正在使用FileStream下载csv文件，但是它覆盖了我现有的文件。而不是创建新的。

 protected void btnGenerate_Click(object sender,EventArgs e)
 {
  using (MemoryStream zipToOpen = new MemoryStream())
  {
  using (var zipArchive = new ZipArchive(zipToOpen,ZipArchiveMode.Update,true))
  {
   List<int> stopWordArray = new List<int>();
   foreach (ListItem listItem in ddlDepot.Items)
   {
   if (listItem.Selected)
    {
    stopWordArray.Add(Convert.ToInt32(listItem.Value.ToString()));
    string FileType = ddlqoutatfileType.SelectedItem.Text;
    DateTime Qotation_Date = Convert.ToDateTime(txtdate.Text).AddDays(3);
    var Qotation_Date_modified = Qotation_Date.ToShortDateString();
    OracleCommand CmdB = new OracleCommand("Select DEPOT_CODE,PRODUCT_CODE,TO_CHAR(TO_DATE(UPLOAD_DATE,'DD/MM/YYYY'),'DDMMYYY') as UPLOAD_DATE,TO_CHAR(TO_DATE(SALES_DATE,'DDMMYYYY') as SALES_DATE,ORDER_QTY,FILE_TYPE,ROUTE_CODE from SCM_SARAS_ORDERS_vw where File_Type = '" + FileType + "' and DEPOT_CODE =" + stopWordArray[0] + " and SALES_DATE = TO_DATE('" + Qotation_Date_modified + "','DD/MM/YYYY')",con);
    CmdB.CommandType = CommandType.Text;
    OracleDataAdapter daB = new OracleDataAdapter();
    DataTable dtB = new DataTable();
    daB.SelectCommand = CmdB;
    daB.Fill(dtB);
    string csv = string.Empty;
    foreach (DataRow row in dtB.Rows)
     {
      foreach (DataColumn column in dtB.Columns)
       {
        csv += row[column.ColumnName].ToString().Replace(",",";") + ',';
       }
       csv += "\r\n";
     }
 var file1 = zipArchive.CreateEntry(ddlInqfileType.SelectedItem.Text.ToString() + ddlDepot.SelectedValue + ".csv");
   using (var entryStream = file1.Open())
   using (var sw = new StreamWriter(entryStream))
   {
    sw.Write(csv);
   }
const string fileName = @"X:\BSD\App Support\NITISH KUMAR\test.Zip";
  using (FileStream fs = new FileStream(fileName,FileMode.Append,FileAccess.Write))
  {
  zipToOpen.Seek(0,SeekOrigin.Begin);
  zipToOpen.CopyTo(fs);
         }
       }
      }
     }
    }
   }
  }
 }

我使用File.Append()，但它仍未创建新文件。