Zend certified PHP/Magento developer

Magento 2 “Class Not Found” external php library

We would like to install external php library in Magento 2

https://github.com/php-sepa-xml/php-sepa-xml

We installed the package with

composer require digitick/sepa-xml:dev-master

In our class we have included

use DigitickSepaTransferFileFactoryTransferFileFacadeFactory;

we ran

php bin/magento setup:di:compile

and got no errors.

When we call up our class we get the error instead

Class DigitickSepaTransferFileFactoryTransferFileFacadeFactory does not exist

Is it an Autoloader problem?
How can we solve?