modulename:
  core_address: 107.101.xx.yy
  core_port: 153759
  core_user: superuser
  core_pass: superpass

services:
    modulename.my_service:
        class: DrupalmodulenamegroupMyService

/**
 * @file
 * Contains DrupalmodulenamegroupMyService.
 */

namespace Drupalmodulenamegroup;

/**
 * MyService.
 */
class MyService{

  public function __construct() { }

  public function getDemoValue() {
    $config =  Drupal::config('modulename.my_service');
    $core_port = $config->get('modulename.core_port');
    return $core_port. 'asdf';
  }

}

/**
 * @file
 * Contains DrupalanothermodulenameControllerMyForm.
 */

namespace DrupalanothermodulenameController;

use DrupalCoreFormFormBase;
use DrupalCoreFormFormStateInterface;
use DrupalComponentUtilityUrlHelper;
use SymfonyComponentDependencyInjectionContainerInterface;

/**
 * MyForm.
 */
class MyForm extends FormBase {

  protected $demoService;

  /**
   * Class constructor.
   */
  public function __construct($demoService) {
    $this->demoService = $demoService;
  }

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container) {
    return new static(
      $container->get('modulename.my_service')
    );
  }

  /**
   * {@inheritdoc}
   */
  public function getFormId() { /** nothing interesting here **/ }

  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state) {
    /** nothing interesting here **/
    return $form;
  }

  /**
   * {@inheritdoc}
   */
  public function validateForm(array &$form, FormStateInterface $form_state){ /** nothing interesting here **/ }

  /**
   * {@inheritdoc}
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {
    // Display result.
    foreach ($form_state->getValues() as $key => $value) {
      drupal_set_message($key . ': ' . $value . '  ' . $this->demoService->getDemoValue()); // i try to print here but didn't happend
    }
  }

}

$config = Drupal::config('modulename.my_service');

$core_port = $config->get('modulename.core_port');

$config = Drupal::service('config.factory')->getEditable('modulename.my_service');
$config->set('modulename.core_port', 153760)->save();

aggregator.admin_settings:
  path: '/admin/config/services/aggregator/settings'
  defaults:
    _form: 'DrupalaggregatorFormSettingsForm'
    _title: 'Feed aggregator settings'
  requirements:
    _permission: 'administer news feeds'

namespace Drupalmodulename;

/**
 * Example Service with config.
 */
class MyService {


  /**
   * Drupal's settings manager.
   */
  protected $settings;

  /**
   * Constructor.
   */
  public function __construct() {
    $this->settings = Drupal::config('modulename.my_service');
  }

}

$this->settings->get('modulename.core_port');

$core_port = $config->get('core_port');
$config->set('core_port', 8888)->save();

core_address: 107.101.xx.yy
core_port: 153759
core_user: superuser
core_pass: superpass