Eror ketika load (memanggil ) librari upload dalam librari buatan sendiri

jadi saya membuat library UploadFile.php, librari tentang apload file gambar berikut librari nya

<?php
class UploadFoto
{

    public function uploadfile($id, $nama_file, $folder, $width, $heigt)
    {
        // ubah file jadi unik
        $ekstensigambar = explode('.', $nama_file);
        $ekstensigambar = strtolower(end($ekstensigambar));
        $namafilebaru = uniqid();
        $namafilebaru .= '.';
        $namafilebaru .= $ekstensigambar;

        $config['upload_path']         =  $folder;
        $config['allowed_types']        = 'gif|jpg|png';
        $config['max_width']            = $width;
        $config['max_height']           = $heigt;
        $config['file_name']            = $namafilebaru;

        $this->load->library('upload', $config);
        // periska jika gambar gagal di upload
        if (!$this->upload->do_upload('gambar_list')) {
            $error = array('error' => $this->upload->display_errors());
            $this->session->set_flashdata("message", "<div class='alert alert-success' role='alert'>Gambar tidak berhasil di upload, mohon periksa ekstensi dan size gambar.</div>");
            redirect("produk/produkEdit?id=$id");
        } else {
            // jika berhasil, akan mengembalikan nama file
            $data = array('upload_data' => $this->upload->data());
            return $config['file_name'];
        }
    }
}

saya sudah load di autoload, dan controller saya

 public function produkUbah()
    {
     $upload = $this->uploadfoto->uploadfile($id, $gambar, 'assets/images/admin/produk_list1', '1000', '1000');
    }

baris 20 yang error

$this->load->library('upload', $config);

tapi error nya Message: Undefined property: UploadFoto::$load