C# delete files being used by another process

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C#

Windows

I am not expert. I am trying to delete the files from the directory at button click. I have windows application which have folders populated in combobox1 and files populated in combobox2. I need to delete the selected folder from combobox1 and files within the folder. I am getting error cannot delete the file as it's being used by another process. Basically application can be used by multiple users and one of the folder I am trying to delete might be listed on the second users combobox. I need to delete the files even if its listed in second users combobox, as I have another logic that doesn't allow the user to select the combobox item selected by first user.

The error is caused because of same filename in another folder(As I have images in all the folders with same names, but different images), it's not caused due to the folder being tried to delete. If user selects the batch that's already deleted, I have logic in place to check if that particular directory no longer exists remove from combobox and move to next batch or first batch if deleted item was last one.

    string batchrem = "";
    selindex02 = comboBox1.SelectedIndex;
    batchrem = comboBox1.Text;

    string dir_name = comboBox1.Text.ToString().Substring(0, 12);
    string path1 = strval + dir_name + "\\";
    //string path1 ="C:\\Project\\" + dir_name + "\\";
    DirectoryInfo di = new DirectoryInfo(path1);
    SqlConnection conn001 = new SqlConnection();
    conn001.ConnectionString = System.Configuration.ConfigurationManager.ConnectionStrings["dbConnection"].ConnectionString;
    SqlCommand comd012 = new SqlCommand("GetBatch", conn001);
    comd012.CommandType = CommandType.StoredProcedure;
    comd012.CommandText = "usp_CAMR_Delete_MarriageInfo";
    comd012.Connection = conn001;
    comd012.Parameters.AddWithValue("@batch_name", comboBox1.Text.ToString().Substring(0, 12));
    comd012.Parameters.AddWithValue("@ERR_CODE", 0);
    comd012.Parameters.AddWithValue("@ERR_MSG", 0);
    comd012.Parameters.AddWithValue("@TABLE_NAME", "");
    try
    {
        SqlConnection con = new SqlConnection();
        con.ConnectionString = System.Configuration.ConfigurationManager.ConnectionStrings["dbConnection"].ConnectionString;
        SqlCommand cmd = new SqlCommand("BatchUpdate", con);
        cmd.CommandType = CommandType.StoredProcedure;
        cmd.CommandText = "usp_CAMR_UnlockedBatchName";
        //cmd.Connection = con;
        con.Open();
        cmd.Parameters.AddWithValue("@Batch_Name", comboBox1.Text.ToString().Substring(0, 12));
        cmd.Parameters.AddWithValue("@lst_mod_userid", Environment.UserName);
        cmd.Parameters.AddWithValue("@ERR_CODE", 0);
        cmd.Parameters.AddWithValue("@ERR_MSG", 0);
        cmd.Parameters.AddWithValue("@TABLE_NAME", 0);
        cmd.ExecuteNonQuery();
        con.Close();
        con.Dispose();
        conn001.Open();
        comd012.ExecuteNonQuery();
    }
    catch (Exception ex)
    {
        {
            oErrorLog.WriteErrorLog(ex.ToString());
        }
        lblerror.Text = "Please contact support team";
    }
    finally
    {
        conn001.Close();
        conn001.Dispose();
        if (di.Exists)
        {
            try
            {
                if (comboBox1.SelectedIndex < comboBox1.Items.Count - 1)
                {
                    comboBox1.SelectedIndex = selindex02 + 1;
                }
                else
                {
                    // comboBox1.Items.Remove(batchrem);
                    comboBox1.SelectedIndex = 0;
                }
                foreach (FileInfo fi in di.GetFiles())
                {

                    System.GC.Collect();
                    System.GC.WaitForPendingFinalizers();
                    fi.IsReadOnly = false;
                    fi.Delete();
                }
                di.Delete();
                comboBox1.Items.Remove(batchrem);
            }
            catch (Exception ex)
            {

                lblerror.Text = ex.Message();
            }
        }
    }
}

What I have tried:

I tried using

System.GC.Collect();
System.GC.WaitForPendingFinalizers();

It works fine if there is only one user using the application