I have a problem with reading from .xlsx (Excel) file. I tried to use:
var fileName = @\"C:\\automated_testing\\ProductsUploadTemplate-2015-10-22.xlsx\";
var
Reading Excel files with OLE provider is possible only if MS Jet engine (MS Access) is installed. I noticed that you decided to use .NET interop to API but this is not a good idea: it requires installed MS Excel and doesn't recommended to use for automation on servers.
If you don't need to support old (binary) Excel formats (xls) and reading XLSX is enough I recommend to use EPPlus library. It provides simple and powerful API for both reading and writing XLSX files (and has a lot of examples):
var existingFile = new FileInfo(filePath);
// Open and read the XlSX file.
using (var package = new ExcelPackage(existingFile)) {
// access worksheets, cells etc
}