Ошибка phpexcel

Пытаюсь данные из php оформить в таблицу excel:

include_once "../phpexcel/PHPExcel.php";

                $phpexcel = new PHPExcel();
                for($j = 0;$j < count($titles);$j++){
                    $string = $titles[$j]['name'];
                    $string = mb_convert_encoding($string, "UTF-8","Windows-1251");
                    $cellLetter = $titles[$j]['cell'] . 1;
                    $phpexcel->getActiveSheet()->setCellValueExplicit($cellLetter, $string, PHPExcel_Cell_DataType::TYPE_STRING);
                }

                $j = 2;
                foreach ($report_data as $elem) {
                    $string = $elem['education_level'];
                    $string = mb_convert_encoding($string, "UTF-8","Windows-1251");
                    $phpexcel->getActiveSheet()->setCellValueExplicit("A$j", $string, PHPExcel_Cell_DataType::TYPE_STRING);
                    $string = $elem['e_program'];
                    $string = mb_convert_encoding($string, "UTF-8","Windows-1251");
                    $phpexcel->getActiveSheet()->setCellValueExplicit("B$j", $string, PHPExcel_Cell_DataType::TYPE_STRING);
                    $string = $elem['discipline_cycle'];
                    $string = mb_convert_encoding($string, "UTF-8","Windows-1251");
                    $phpexcel->getActiveSheet()->setCellValueExplicit("C$j", $string, PHPExcel_Cell_DataType::TYPE_STRING);
                    $string = $elem['year'];
                    $string = mb_convert_encoding($string, "UTF-8","Windows-1251");
                    $phpexcel->getActiveSheet()->setCellValueExplicit("D$j", $string, PHPExcel_Cell_DataType::TYPE_STRING);
                    $phpexcel->getActiveSheet()->setCellValueExplicit("E$j", $elem['course']);
                    $phpexcel->getActiveSheet()->setCellValueExplicit("F$j", $elem['semestr']);
                    $phpexcel->getActiveSheet()->setCellValueExplicit("G$j", $elem['flow']);
                    $string = $elem['module'];
                    $string = mb_convert_encoding($string, "UTF-8","Windows-1251");
                    $phpexcel->getActiveSheet()->setCellValueExplicit("H$j", $string, PHPExcel_Cell_DataType::TYPE_STRING);
                    $string = $elem['discipline'];
                    $string = mb_convert_encoding($string, "UTF-8","Windows-1251");
                    $phpexcel->getActiveSheet()->setCellValueExplicit("I$j", $string, PHPExcel_Cell_DataType::TYPE_STRING);
                    $phpexcel->getActiveSheet()->setCellValueExplicit("J$j", $elem['credits']);
                    $phpexcel->getActiveSheet()->setCellValueExplicit("K$j", $elem['all_hours']);
                    $phpexcel->getActiveSheet()->setCellValueExplicit("L$j", $elem['lections']);
                    $phpexcel->getActiveSheet()->setCellValueExplicit("M$j", $elem['practices']);
                    $phpexcel->getActiveSheet()->setCellValueExplicit("N$j", $elem['laboratory']);
                    $phpexcel->getActiveSheet()->setCellValueExplicit("O$j", $elem['srsp']);
                    $phpexcel->getActiveSheet()->setCellValueExplicit("P$j", $elem['srs']);
                    $phpexcel->getActiveSheet()->setCellValueExplicit("Q$j", $elem['control_work']);
                    $string = $elem['department'];
                    $string = mb_convert_encoding($string, "UTF-8","Windows-1251");
                    $phpexcel->getActiveSheet()->setCellValueExplicit("R$j", $string, PHPExcel_Cell_DataType::TYPE_STRING);
                    $string = $elem['availability_teacher'];
                    $string = mb_convert_encoding($string, "UTF-8","Windows-1251");
                    $phpexcel->getActiveSheet()->setCellValueExplicit("S$j", $string, PHPExcel_Cell_DataType::TYPE_STRING);
                    $string = $elem['clin_department'];
                    $string = mb_convert_encoding($string, "UTF-8","Windows-1251");
                    $phpexcel->getActiveSheet()->setCellValueExplicit("T$j", $string, PHPExcel_Cell_DataType::TYPE_STRING);
                    
                    $j++;
                }

                for($i = 0;$i < count($titles);$i++){
                    $columnLetter = $titles[$i]['cell'];
                    $phpexcel->getActiveSheet()->getColumnDimension($columnLetter)->setWidth(40);
                }

                $page = $phpexcel->setActiveSheetIndex();
                $page->setTitle("Название");
                $objWriter = PHPExcel_IOFactory::createWriter($phpexcel,'Excel2007');
                $filename = "Название.xlsx";
                $objWrirer->save($filename);

Но получаю следующую ошибку: Fatal error: Uncaught Error: Call to a member function save() on null in D:\open_server\OpenServer\domains\filepath:249 Stack trace: #0 {main} thrown in