Not all instances of Excel application closing after running code

This is the code, I have seen in several other places to close instances of the objects with Marshal.FinalReleaseComObject(...)

This method is called everytime a successful message is sent.

    public static Excel.Workbook MyBook = null;
    public static Excel.Application MyApp = null;
    public static Excel.Worksheet MySheet = null;

    private static void SuccessLog(string communicationMethod, string portNumber, int messageDelay)
    {
        Console.WriteLine(Environment.NewLine);
        DateTime startTime = DateTime.Now;
        string trimDate = Convert.ToString(startTime.ToShortDateString()).Replace('/', '_');
        string folder = @"C:\Temp\";
        string fileName = Convert.ToString(trimDate);
        string message = "Message Sent At: " + Convert.ToString(startTime) + ", via " + communicationMethod + ", at port # " + portNumber + "." + Environment.NewLine;
        string fullPath = folder + fileName;

        MyApp = new Excel.Application();
        MyApp.Visible = false;
        var workbooks = MyApp.Workbooks;
        if (!File.Exists(fullPath + ".xlsx"))
        {
            MyBook = workbooks.Add();
            MySheet = MyBook.Sheets[1]; // Explicit cast is not required here
            int lastRow = MySheet.Cells.SpecialCells(Excel.XlCellType.xlCellTypeLastCell).Row;
            MySheet.Cells[lastRow, 1] = "asdfsa";
            MySheet.Cells[lastRow, 2] = "asdfsa";
            MySheet.Cells[lastRow, 3] = "asdfsa";
            MySheet.Cells[lastRow, 4] = "asdfsa";
            
            MyBook.SaveAs(fullPath);
            MyBook.Close(0);
        }
        else
        { 
            MyBook = workbooks.Open(fullPath + ".xlsx");
            MySheet = MyBook.Sheets[1]; // Explicit cast is not required here

            int lastRow = MySheet.Cells.SpecialCells(Excel.XlCellType.xlCellTypeLastCell).Row;
            lastRow ++;
            MySheet.Cells[lastRow, 1] = "exists?";
            MySheet.Cells[lastRow, 2] = "exists?";
            MySheet.Cells[lastRow, 3] = "exists?";
            MySheet.Cells[lastRow, 4] = "exists?";
            MyBook.Save();
            MyBook.Close(0);
        }

Here is where I am trying to close all of the Objects that I am creating. I think I may possibly be missing some of the objects.

        MyApp.Quit();
        Marshal.FinalReleaseComObject(MySheet);
        Marshal.FinalReleaseComObject(MyBook);
        Marshal.FinalReleaseComObject(MyApp);
        Marshal.FinalReleaseComObject(workbooks);
        Console.WriteLine("Log has been successfully updated or added at: " + fullPath);
        Console.WriteLine("Next message will be sent in: " + MessageDelay + " seconds. (Specified in Config.)");
   }