trying to use phpSpreadsheet

I am trying to allow a user to upload and import the data from an excel file into my mysql table. To do this I am trying to use phpSpreadsheet.

I installed phpSpreadsheet with Composer. I then put their sample function into my controller in one of the functions. I can upload the file fine using the CI upload lib. The require statemenrt works good ( at least no errors!). The use statements don't work at all so I commented them out. The new Spreadsheet statement complains that


A PHP Error was encountered
Severity: Error
Message: Class 'Spreadsheet' not found
Filename: controllers/Configure.php


How can I get this to work? 
 
require 'vendor/autoload.php';

//use PhpOffice\PhpSpreadsheet\Spreadsheet;
//use PhpOffice\PhpSpreadsheet\Writer\Xlsx;

$spreadsheet = new Spreadsheet();
$sheet = $spreadsheet->getActiveSheet();
$sheet->setCellValue('A1', 'Hello World !');

$writer = new Xlsx($spreadsheet);
$writer->save('hello world.xlsx');

proof that an old dog can learn new tricks