This is a valid point and obviously something I should be wary of.

I'm not sure about the legal situation, but isn't it so that they cannot serve me a 'Betreibung' until after they have sent me the bill by regsitered post. As long as I always pay up when it comes to that they can't get me? Or am I being too simplistic here?

Of course I wouldn't want to play with fire and let it come to that. This question is more out of curiosity.