While thread.join() time when I click export button even enabled=false; firing finally when the thread stops

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C#

Dear experts,

for example in my c# windows application, in export button i am starting one thread,
here i am exporting sql data to csv file. Its working fine.

When user hits the cancel button i disable the export button and stoping the thread, after deleting the file i am enabling the Export button.

while thread stops takes some time, at this moment of time when i click already disabled export button-its firing after the thread stops.

Here is my code
Export Button

private void btn_Export_Click(object sender, EventArgs e)
        {
            ErrorMessage1.Visible = false;
            ErrorMessage2.Visible = false;
            LAHDALClass objLAHDALClass = new LAHDALClass();
            Savingpath();

            if (cmb_ProjectName.Text== "Create New Project")
            {
                MessageBox.Show("Please select Project Name from the Project Name dropdown");

                return;
            }
            if (!string.IsNullOrEmpty(cmb_TrasnformedDS.Text))
            {
                Valid = true;
            }
            else
            {
                MessageBox.Show("Please select a transformed dataset from the Transformed Dataset Name dropdown.");
                cmb_TrasnformedDS.Focus();

                return;
            }
            if (!string.IsNullOrEmpty(cmb_ProjectName.Text))
            {
                Valid = true;
            }
            else
            {
                MessageBox.Show("Please select Project Name from the Project Name dropdown");
                cmb_ProjectName.Focus();

                return;
            }

            if (Valid)
            {

                btn_Export.Enabled = false;

                cmb_TrasnformedDS.Enabled = false;
                cmb_ProjectName.Enabled = false;
                DisableImport_TabPage();
                DisableTransform_TabPage();
                DisableInputfiletypeRB();
                lb_Progress.Location = new System.Drawing.Point(55, 18);
                lb_Progress.Text = "Exporting Started...";
                panel1.Visible = true;
                pb_RunningImage.Visible = true;
                Projectname = cmb_ProjectName.Text;
                TrasnformedDS = cmb_TrasnformedDS.Text;
                ExportedFilePath = ConfigurationManager.AppSettings["ExportedFiles"].ToString();
                ExportedFilePath = ExportedFilePath + Projectname +"\\"+ TrasnformedDS + ".csv";
                if (rb_FlatFile.Checked & rb_WH.Checked)
                {
                    rb_HW.Enabled = false;
                }
                if (rb_FlatFile.Checked & rb_HW.Checked)
                {
                    rb_WH.Enabled = false;
                }
                if (File.Exists(ExportedFilePath))
                {

                    panel1.Visible = false;
                    btn_TrnsCancel.Enabled = false;

                    if (MessageBox.Show("The transformed table already exists in the selected project folder.\nPlease create a new project folder to be able to export the data again.", "Message Alert", MessageBoxButtons.OK, MessageBoxIcon.Warning) == DialogResult.OK)
                    {
                        FunctionEnable("EnableUIcontrols");
                    }
                }

                else
                {
                    CsvfileWriter = new StreamWriter(ExportedFilePath);

                    thrThreadExportProcess = new Thread(new ThreadStart(startExport));

                    thrThreadExportProcess.Start();
                    thrThreadExportProcess.IsBackground = true;

                }
            }
        }
private void startExport()
        {
            
            Savingpath();
            LAHDALClass objIEDDAL = new LAHDALClass();
            try
            {
                
                EnableCancelButton("EnableUIcontrols");
                Thread.Sleep(0);
                
                Stopwatch swra = new Stopwatch();
                swra.Start();

                objIEDDAL.ExportData(TrasnformedDS, Projectname, CsvfileWriter);
                swra.Stop();
                Console.WriteLine(swra.ElapsedMilliseconds);
                
            }
            catch (Exception ex)
            {
                throw ex;
                
            }
            
        }

cancel button code

private void btn_ExportCancel_Click(object sender, EventArgs e)
        {
            
            LAHDALClass objIEDDAL = new LAHDALClass();
            
            //btn_Export.Visible=false;
            //btn_ExportCancel.Visible = false;
             btn_Export.Enabled = false;
            btn_ExportCancel.Enabled = false;
            
          

            try
            {
                
                stopProcess = true;
                if (stopProcess == true & thrThreadExportProcess.IsAlive)
                {
                    
                    this.thrThreadExportProcess.Abort();
                   
                    
                    thrThreadExportProcess.IsBackground = false;
                    //thrThreadExportProcess = null;
                    pb_RunningImage.Visible = false;
                   
                   lb_Progress.Text = "Canceling...";
                       Application.DoEvents();
                        thrThreadExportProcess.Join();
                        thrThreadExportProcess = null;
                        

                        objIEDDAL.CancelExport(TrasnformedDS, Projectname, usersSavingPath);//, ExportTempTableName);
                       
                        rb_HW.Enabled = true;
                        rb_WH.Enabled = true;
                        panel1.Visible = false;
                    }
                    EnableImport_TabPage();
                    EnableTransform_TabPage();
                    EnableInputfiletypeRB();
                    cmb_TrasnformedDS.Enabled = true;
                    cmb_ProjectName.Enabled = true;
                    cmb_ProjectName.Text = "";
                    btn_Export.Enabled = true;

                    
                }
          
            catch (Exception ex)
            {
                throw ex;
             
            }
            
        }

Plese give me your ideas.