Zend certified PHP/Magento developer

save custom billing attribute value from order

I have problem with save custom billing attribute.
I added attribute into Customer Address Entity table.
all field of billing address are save to db without my custom attribute.
My attribute are save in order table,if logged customer edit field it saved too.
But if logged customer add new billing address the attribute (billing adress extension attribute) not saved.
I use https://codeblog.experius.nl/magento-2-add-extra-billing-or-shipping-field-to-the-checkout/ instruction to build my module.
And USE this observer:
‘<?php
namespace VenigeCustomAttObserver;

use MagentoFrameworkEventObserverInterface;
use MagentoFrameworkEventObserver;
use MagentoCustomerApiCustomerRepositoryInterface;

class SaveCustomFieldsInOrder implements ObserverInterface
{

public function execute(MagentoFrameworkEventObserver $observer) {
    $order = $observer->getEvent()->getOrder();
    $quote = $observer->getEvent()->getQuote();

           $writer = new ZendLogWriterStream(BP . '/var/log/SaveCustomFieldsInOrder.log');
            $logger = new ZendLogLogger();
            $logger->addWriter($writer);
            //My custom attribute has value in this moment
            $logger->info('SaveCustomFieldsInOrder: '.$quote->getBillingAddress()->getExtensionAttributes()->getEik()); //My custom attribute has value in this moment
     if ($quote->getBillingAddress()) {
          $order->getBillingAddress()->setEik($quote->getBillingAddress()->getExtensionAttributes()->getEik());
         //$customerAddress->setEik($quote->getBillingAddress()->getExtensionAttributes()->getEik());
          
      }
      if (!$quote->isVirtual()) {            
          $order->getShippingAddress()->setEik($quote->getShippingAddress()->getEik());
      }
      

    return $this;
}
    
   

}’

how to save my custom billing address attribute value into customer address in database.