Activate worksheet C# Excel

I have tried many things to try and get Excel to have a selected sheet in an Add-In.  So everything works in my code until I get to line: xlApp.ActiveWorkbook.Sheets[1].Activate();

Passing the name of the sheet to activate would be the best route to success but at this point I am trying anything to get this to work.

Here is some of the code that I have tried so far:

       const String Config = "Config";
        private Microsoft.Office.Interop.Excel.Application app = null;
        private Microsoft.Office.Interop.Excel.Worksheet worksheet = null;
       
        /// <summary>
        /// Read the config sheet cells
        /// </summary>
        /// <param name="Row">Row to Read</param>
        /// <param name="Col">Column to Read</param>
        /// <returns></returns>
        public String CellValueStr(
                                    Int64 Row
                                  , Int64 Col
                                    )
        {
            String cellValue = String.Empty;
            String CurrentSheet = Config;

            var xlApp = new Microsoft.Office.Interop.Excel.Application();
            Excel.Workbooks xlWorkbooks = xlApp.Workbooks;

            xlApp.ActiveWorkbook.Sheets[1].Activate();
            xlWorkbooks.Sheets[1].Activate();
            xlSheet.Activate();
           
            xlWorkbook = xlWorkbooks.Open(@"C:\filename.xlsx");



            //Excel.Worksheet sheet = (Excel.Worksheet)this.app.Worksheets[CurrentSheet];
            //Excel.Worksheet sheet = (Excel.Worksheet)ActiveWorkbook.Sheets["Sheet2"];

            //((Excel.Worksheet)this.app.ActiveWorkbook.Sheets[1]).Select();
            //((Excel.Worksheet)this.Application.ActiveWorkbook.Sheets[1]).Select();
            //sheet.Select(Type.Missing);

            //Worksheet sheet = (Worksheet)Workbook.Sheets["ASD"];
            //sheet.Select(Type.Missing);

            System.Data.OleDb.OleDbConnection MyConnection;

            MyConnection = new System.Data.OleDb.OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + tbFileName.Text + ";Extended Properties=Excel 12.0;");

            Microsoft.Office.Interop.Excel.Application xlApp = new Microsoft.Office.Interop.Excel.Application();

            //get the workbook
            Microsoft.Office.Interop.Excel.Workbook excelBook = xlApp.Workbooks.Open(tbFileName.Text);

            //get the first worksheet
            Microsoft.Office.Interop.Excel.Worksheet wSheet = excelBook.Sheets.Item[1];


            var xls = new Microsoft.Office.Interop.Excel.Application();


            xls.ActiveWorkbook.Sheets[CurrentSheet].Activate();

            xls.ActiveWorkbook.Sheets[1].Activate();
            xls.ActiveSheet();

            cellValue = (string)(worksheet.Cells[Col, Row] as Excel.Range).Value;

            return cellValue;
        }

Visual Studio 2015 and Excel 2016, 2013 and 2010

Please let me know if I am losing my mind as it seems none of the examples on this site work out?  (More coffee?)

So as an end result I would like to retrieve various values in certain sheets to perform actions based on these values.  The business currently has this functionality but it is written in VBA which is not going to work long term for us.

Thanks in Advance!