public function call($method, $params=[]) {
    $header = $this->generateWSSecurityHeader($this->user, $this->password);
    $response = $this->__soapCall($method, sizeof($params) > 0 ? [$params] : [], null, $header);
    // in document/literal style the "return" parameter holds the result
    return property_exists($response, 'return') ? $response->return : $response;
  }