API响应提取方法不称为CI

I have bad english, but i hope I can explain you my situation. I have payment controller and two methods.

class payment extends MX_Controller{
    public function __construct(){
        parent::__construct();
        $this->load->model(get_class($this) . "_model", "model");
    }

    public function pay(){
        //Gets form data and sends to payment service
    }

    public function check(){
        //Gets response from payment service and acts according payment                         
        //status
    }
}

First sends data to payment service and second have to do something according payment response scenario.

So in my payment cpanel I wrote this url "htts://my-domain.do/payment/check" for response. The first method works successfully, it sends all needed data, but my second "check()" method does not called.

When I simply write https://my-domain/payment/check it still not working, but when I call like this https://my-domain/index.php/payment/check it works. My .htaccess also configured.

I use CI 3. Is there any one who had the problem like this.

My .htaccess file look like

RewriteEngine On
Options +FollowSymLinks
Options -Indexes
RewriteCond %{SCRIPT_FILENAME} !-d  
RewriteCond %{SCRIPT_FILENAME} !-f
RewriteRule . index.php [L,QSA]

And in app/config/config.php

$config['index_page'] = '';