In Germany the law is very clear. If you declare yourself as self-employed you must operate as a business. The key test authorities apply is to check how many customers the self employed person has served in the last tax year. If the answer is one, you cannot deemed as self employed. The bad news is the offence has been committed by the disguised employee, not the disguised employer. Ryanair, or any other linked company are not on the hook.
You've wilfully declared yourself as self employed in order to gain a financial advantage whilst not actually exhibiting any semblance of a business, which is fraud... It's the harsh reality, I've been through it
When you sign such a service contract, the other party is perfectly aware that you, not them are on the hook for social costs and taxes due, no matter what. The other party rests on the defence that they took all reasonable steps to ensure you were self employed and assumed you would comply with the applicable laws. Its a horrible situation to be in.