Closed my account with an explanation…
Closed my account with an explanation "read our conditions" referring me to the guidelines online (no exact reason given). Fortunately, only 20 EUR were on my account (which have never been given back, btw).

P.S. (Added after N26's reply below) and here you go: check out the explanation I was given for closing my account and stealing 20 EUR left on it. Translation: we can close your account whenever we want; we will not bother explaining exactly the reason (it may be your last name), and we will even not reimburse the balance you had on your account. Pathetic