Interop.Excel always saving in default path even specifying the path manually for Office 365

Trying to create an Excel file using Office.Interop.dll (15.0.4795.1001).But it is taking the default file path instead of the path which set manually.

            if (extensionObj != null)

            {

                relativeExcelPath = string.Concat(System.IO.Path.GetDirectoryName(extensionObj.WorkflowPath), "\\", workflowName);

            }

            // Checking if excel file is present in workflow running directory, if exists then open the file in workflow running directory otherwise 

            // continue with user supplied path.

            excelPath = System.IO.File.Exists(relativeExcelPath) ? relativeExcelPath : context.GetValue(Path);
```public static void SaveExcel(excel.Workbook myWorkBook)

{

    excel.Application myApp;

    myApp = new excel.Application();

    myWorkBook.Save()