Subscription Scam: How do I get out?

My wife has fallen prey to one of these lottery scams where she just wanted to sign up to win some prize, and now people have called her to say that she has an expensive abo to get "travel vouchers".

I just learned that today they called and got her to tell them her bank account number for an Einzugsermächtigung. But she does not know the name of the company, has no email, nothing. She only has some "Hotline" number. How do we get out of this? Or at least ensure that the damage is a small as possible.

(And why is this even LEGAL? I can't understand why this sort of thing is allowed!!)

Thanks very much for any assistance you can provide <3