This is a follow-up to this question:
A year has passed, and the organization behaved exactly the same. They sent me a fine to pay, without sending me any notice at all before.
Now, since I don't believe that these people are doing they work right, I did find the obligations one is supposed to honor after signing their "membership", and checked them all. I strongly believe that contracts work both sides, and as it turns out, in their constitution it is written:
Die Mitgliederversammlung hat mindestens einmal im Jahr stattzufinden. Sie wird vom Vorstand einberufen. Die Einberufung hat schriftlich mit einer Frist von mindestens zwei Wochen unter Angabe der Tagesordnung, des Tagungsortes und des Zeitpunktes zu erfolgen. Gleichzeitig ist die Aufsichtsbehörde zu benachrichtigen. Das Einladungsschreiben ist jedem Mitglied einzeln zuzustellen und gilt als zugegangen, wenn es an die letzte vom Mitglied benannte Adresse gerichtet ist.
Which if translated, means (well, the important part) that they have to invite every member to a meeting at least once a year. They never did, and apparently last meeting was more than 1 year ago.
Is there any law that will let me avoid paying at all (not the fine, not the yearly quota) since they:
a) didn't send me a Rechnung (invoice)
b) broke the article of their constitution
EDIT: After reading the selected answer, I ended up sending an email to the German watchdog authority (Oberfinanzdirektion) of the region I live in explaining the situation (I'm no lawyer) and making it clear that I didn't also use the services of the Lohnsteuerhilfeverein this year. They actually followed up, and today I received the confirmation that my membership-quota for this year is not to be paid. The email sounded like the Lohnsteuerhilfeverein was doing me a favour, but since it came from them and not from the authority, I think they are indeed in the wrong.