/**
  * Update subscriber details
  *
  * @param string $emailAddress 
  * @param string $contactName 
  * @return void
  * @author Dan Chadwick
  */
 public function update_subscriber($email_address, $contact_name)
 {
     $cm = new CampaignMonitor($this->api_key);
     // Optional statement to include debugging information in the result
     $cm->debug_level = 0;
     // This is the actual call to the method
     $result = $cm->subscriberAddAndResubscribe($email_address, $contact_name);
     if ($result['Result']['Code'] == 0) {
         return true;
     } else {
         Kohana::log('error', 'Campaign Monitor Error : ' . $result['Result']['Message']);
         return false;
     }
 }