public static void ImportToSql(string excelfilepath)
        {
            string ssqltable = "TABHD";
            string myexceldataquery = "SELECT * FROM [dbo_TABHD]";
            try
            {
                string sexcelconnectionstring = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source =" + excelfilepath + "; Extended Properties=\"Excel 12.0; HDR=Yes; IMEX=2\"";
                string ssqlconnectionstring = @"server = itfriend;Database=HD;integrated security = true";
 
                //execute a query to erase any previous data from our destination table
                string sclearsql = "delete " + ssqltable;
                INSERTING IT.INSTEAD I WANT TO UPDATE TABLE DATA"
                SqlConnection sqlconn = new SqlConnection(ssqlconnectionstring);                
 
                OleDbConnection oledbconn = new OleDbConnection(sexcelconnectionstring);
                OleDbCommand oledbcmd = new OleDbCommand(myexceldataquery, oledbconn);
                oledbconn.Open();
                OleDbDataReader dr = oledbcmd.ExecuteReader();
                SqlBulkCopy bulkcopy = new SqlBulkCopy(ssqlconnectionstring);
                bulkcopy.DestinationTableName = ssqltable;
 
                bulkcopy.WriteToServer(dr); // Eror in here: "Not a legal OleAut date"
 
                Console.WriteLine(".xlsx file imported succssessfully into database.", bulkcopy.NotifyAfter);
                oledbconn.Close();
            }
            catch (Exception ex)
            {
                //handle exception
                MessageBox.Show(ex.Message.ToString(), "Warning !");
            }
        }