Problem with Redis: Fatal error: Class 'redis' not found

I use modelsCache such way:

    $di->setShared('modelsCache', function () {
      $frontCache = new DataFrontend([
          'lifetime' => 3600 * 24 * 7
      ]);

      $redis = new \Phalcon\Cache\Backend\Redis($frontCache, [
          'host' => $this->get('config')->redis->host,
          'port' => $this->get('config')->redis->port,
          'auth' => $this->get('config')->redis->password
      ]);

      return $redis;
    });

and I got error:

    Fatal error: Class 'redis' not found in /home/www/apps/models/entities/Company/Company.php on line 421

This line is:

    $company = Company::findFirst([
            'cache' => 'company_cache_key'
    ]);

This code return true:

    class_exists('\Phalcon\Cache\Backend\Redis');

I suspect there is problem with some Phalcon Framework class which handle Redis. But I have no idea how to fix it. Other libraries which use Redis work fines, generally Redis server works good. Any idea?