Degiro refuses to give out control numbers to vote by proxy stating that it is due to the "general structure" of the company. What do they mean by that?

As the title states, the reason that Degiro is giving regarding their refusal to give out the control number of our shares, is that the "general structure" of the company doesn't allow it.

What do they mean by that? What kind of structure can a broker have that prevents them from giving their clients their control number so they can vote themselves? What happens if I, as a shareholder, want to attend, in person, to the shareholders meeting? Shouldn't they facilitate some kind of identification or control number that allows me to exercise my right to attend? What is the legality regarding their refusal to facilitate my right to cast a secret vote through the official channels opened by the company of which I'm a shareholder?

I'm in contact with them through email trying to answer these questions but until they respond I would love to know if someone here can help me understand this situation better. Personally I don't see any sensible reason by which they couldn't be able to facilitate the proxy vote control number to their clients. To vote in our behalf they need that number, so why don't facilitate it to us so we can do it ourselves?