How to create multiple CSV file in ASP .Net - asp.net

Question

I want to create multiple CSV file for every drop down Selected value. Even-though while debugging i can notice csv is appending for different drop down value but not writing another CSV file. do not know why and where i am doing mistake.
When i remove using block, and for second time its throwing error :
The process cannot access the file 'File path' because it is being used by another process.
I believe need to store all files on server but again same issue
i have added code to solve error but no change;
if (File.Exists(filePath))
File.Delete(filePath);
Button code
protected void btnGenerate_Click(object sender, EventArgs e)
{
List<int> stopWordArray = new List<int>();
foreach (ListItem listItem in ddlDepot.Items)
{
if (listItem.Selected)
{
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,'DD/MM/YYYY'), 'DDMMYYYY') as SALES_DATE, ORDER_QTY, FILE_TYPE, ROUTE_CODE from SCM_SARAS_ORDERS_vw where File_Type = '" + FileType + "' and DEPOT_CODE =" + listItem.Value + " 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";
}
string fileName = "myfile.csv";
string filePath = Server.MapPath("~/file" + fileName);
using (StreamWriter sw = new StreamWriter(filePath, false))
{
sw.Write(csv);
}
}
}
}

Answer 1

I am not sure what do you mean about follow problem.
#but not writing another CSV file#
in your code, obviously, you wrote same file in the loop; why do not you change it to
string fileName = "myfile"+listItem.Value+".csv";//change filename?
string filePath = Server.MapPath("~/file" + fileName);
using (StreamWriter sw = new StreamWriter(filePath, false))
{
sw.Write(csv);
}