There is no law in Place (that I now off), that forces to give you a business account (or any account).
Many smaller Banks even State that they may disallow you to open an account for any given reason.
However many Banks have a voluntary commitment in place to allow everyone to have at least on account (asset based only). The so called "Jedermann-Konto".
But precedent cases have shown, that they are allowed to close even this account for basically any given reason:
Die Klage ist jedoch unbegründet, da das von der Klägerin behauptete Rechtsverhältnis nicht besteht. Die Beklagte ist unter keinem rechtlichen Gesichtspunkt verpflichtet, der Klägerin ein Konto auf Guthabenbasis nebst der Möglichkeit zum Onlinebanking zur Verfügung zu stellen.
The lawsuit is unfounded, because the the legal relationship does not exist. The defendant is not on any legal obligation to make an account on a prepaid basis, together with the opportunity for online banking.
So, I'm Sorry.