im using following code to send sms to all the students in the database

```
private void btnsend_Click(object sender, EventArgs e)
    {
        foreach (Control c in Controls)
        {
            c.Enabled = false;
        }
        if (!bgw.IsBusy)
        {
            bgw.RunWorkerAsync();
        }
    }
    private void bgw_DoWork(object sender, DoWorkEventArgs e)
    {
        for (int i = 0; i < dt.Rows.Count; i++)
        {
            Invoke((MethodInvoker)delegate()
            {
                using (var sp = new SerialPort(cbcomport.Text))
                {
                    sp.Open();
                    sp.WriteLine("AT" + Environment.NewLine);
                    sp.WriteLine("AT+CMGF=1" + Environment.NewLine);
                    sp.WriteLine("AT+CMGS=\"" + dt.Rows[i]["PhoneNo"] + "\"" + Environment.NewLine);
                    sp.WriteLine(tbsms.Text + (char)26);
                    if (sp.BytesToRead > 0)
                    {
                        tbsentto.Text = i + 1 + " of " + dt.Rows.Count;
                    }
                }
            });
            Thread.Sleep(5000);
        }
    }
    private void bgw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        foreach (Control c in Controls)
        {
            c.Enabled = true;
        }
    }

```

my question is: during sms is being sent to the students if an exception occurs e.g The port 'COM5' does not exist. i want to display the same system message to the user with buttons retry and cancel. if having resolved the problem. i.e having plugged in the device user presses retry button i want to resume the thread from the same point and if user presses cancel button i want to stop the paused thread.