how to get range in excel sheet using openxml and c#

I have to read Excel(.xlsx) file. I am using OpenXML NuGet pkg. I am trying to get the range(xlRange), so I can fetch the data from a particular cell. But not getting success. This code is created in console environment.

static void Main(string[] args)
{    
    bool flagDataError = false;
    string sDuplicateRows = string.Empty;
    string sCreatedRows = string.Empty;
    string sFileTypeError = string.Empty;
    string filepath = @"C:\test.xlsx";
    var fileName = Path.GetFileName(filepath);
    var fileExtension = Path.GetExtension(filepath);
    if ((fileExtension != ".xlsx") && (fileExtension != ".xls"))
        sFileTypeError = "Invalid file. \n\nPlease browse a correct Excel file to upload.";
    else
    {          
        using (SpreadsheetDocument doc = SpreadsheetDocument.Open(filepath, false))
        {
            WorkbookPart workbookPart = doc.WorkbookPart;
            WorksheetPart worksheetPart = workbookPart.WorksheetParts.First();
            SheetData sheetData = worksheetPart.Worksheet.Elements<SheetData>().First();


            List<AxisData> data = new List<AxisData>();
            for (int i = 5; i <= 16; i++)
            {
                for (int j = 2; j <= 13; j++)
                {
                    AxisData axisDetails = new AxisData();
                    axisDetails.ProductCode = "AXIS " + xlRange.Cells[i, 1].Value;
                    axisDetails.ContractPeriod = Convert.ToDateTime(xlRange.Cells[4, j].Value);
                    axisDetails.SettlePrice = Convert.ToDecimal(xlRange.Cells[i, j].Value);
                    axisDetails.EffectiveStartDate = efectiveStartDate;
                }
                }
            }
        }
    }
}
}