Problem to save excel file, not getting updated value of excel file in gridview

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C#

ASP.NET

I have excel file in that I am doing some calculation, when I take values from user on that values doing calculation, calculated cells I want to show back on web page in gridview, but I am not getting updated values of cells(result) it showing old one.

while debugging if I open excel file and save and close then I am getting updated values of cell so it seems like excel file is not saving.

to update excel I am using OLEDB in C#, ASP.net

here is code snap:

 if (strFileType.Trim() == ".xls")
                {
                    connString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + Npath + ";Extended Properties='Excel 12.0;HDR=No;'";

                }
                else if (strFileType.Trim() == ".xlsx")
                {
                    connString = "Provider=Microsoft.ACE.OLEDB.8.0;Data Source=" + Npath + ";Extended Properties=\"Excel 8.0;HDR=No;IMEX=1\"";
                }

//Updating data 
//on Calculate Button
conn = new OleDbConnection(connString);
cmd.CommandText = "update [ROLLED SECTION$C5:C5] set F1='" + txtBeamLength.Text + "'";
            cmd.ExecuteNonQuery();
//result 
//on Show result button
string qry = "SELECT * FROM [" + ddlSectionType.Text + "$A20:F25]";
 cmd = new OleDbCommand(qry , conn);
            OleDbDataAdapter da = new OleDbDataAdapter();
            da.SelectCommand = cmd;
            DataSet ds = new DataSet();
            da.Fill(ds);
GridView1.DataSource = ds;
GridView1.DataBind();

I am using ASP.net and c # for back end.
Please help me in this I am trying to resolve this issue from long time.....

What I have tried:

Using Interop excel file object its not saving file after uploading site on server and I don't want to show this excel to user.