Upgrade to version 3x breaks customisations

Hi,
Upgrading to version 3x has broken customisations we have in our site.
I expect this is as in version 3.x there is “New architecture implemented” (I see in the readme.txt). I have made a request for the previous version via SIB support.

From what I see in our custom code, the plugin structure has completely changed.
We are calling :

if ( ! class_exists( ‘SIB_Model_Contact’ ) ) {
require_once ABSPATH.’wp-content/plugins/woocommerce-sendinblue-newsletter-subscription/model/model-contacts.php’;
}
if ( ! class_exists( ‘Mailin_Woo’ ) ) {
require_once ABSPATH.’wp-content/plugins/woocommerce-sendinblue-newsletter-subscription/includes/mailin.php’;
}
if ( ! class_exists( ‘SibApiClient’ ) ) {
require_once ABSPATH.’wp-content/plugins/woocommerce-sendinblue-newsletter-subscription/includes/SibApiClient.php’;
}
require_once ABSPATH.’wp-content/plugins/woocommerce-sendinblue-newsletter-subscription/model/model-country.php’;
require_once ABSPATH.’wp-content/plugins/woocommerce-sendinblue-newsletter-subscription/includes/wc-sendinblue.php’;
require_once ABSPATH.’wp-content/plugins/woocommerce-sendinblue-newsletter-subscription/includes/wc-sendinblue-sms.php’;
require_once ABSPATH.’wp-content/plugins/woocommerce-sendinblue-newsletter-subscription/includes/wc-sendinblue-smtp.php’;
require_once ABSPATH.’wp-content/plugins/woocommerce-sendinblue-newsletter-subscription/includes/wc-sendinblue-api.php’;

These files no longer exist in the new version ??