It’s easy. You have a DS Lite connection. And with that, no publicly accessible IP4 address works. It doesn’t help to call and ask for one. Here you can read why that is: Link
What you could do is also switch to the business tariff. It is practically not more expensive, but you can book a fixed IP4 address there. For €5 per month.
I had an IP4 address activated on my connection years ago. At that time, however, these DS Lite connections were not common. In the meantime, new connections are almost exclusively assigned with DS Lite. Sorry if I have to say it so directly. With DS Lite you’ve played the ass card (Arschkarte).
Anbei ein Screenshot aus meiner FB:
