ion auth with CI2.x

You might want to move to CI 3.1.8, PHP 7.0 and the latest Ion Auth release.

this is the code :
$this->db->select('column name');
$this->db->from('oc_access_token');
$this->db->where('token',$access_token);
$this->db->where('atuser_id',$user_id);
$query = $this->db->get();
$result = $query->row();

the data(user id  and acess token) exiost in db but result is always null can you help me why result is null