Fine without any reminder, after not having honored contract obligations

Question

This is a follow-up to this question:

Fine and contract-renew after NOT receiving an invoice

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.

Answer 1

Please note that I can't provide legal advice and consider the following as suggestions you can and should discuss with a lawyer of your choice:

You are probably member of a tax-advisory association (Lohnsteuerhilfeverein). These associations can only advise its members on their tax declarations. Therefore you are indeed a member, not a "member". As a member you are presumably obliged to pay a yearly membership fee, and from your initial question I infer that the membership cannot be terminated before three years have passed.

That and when you have to pay your fee is most likely provided for in the association's constitution. Payment of the fee does not depend on an invoice, because the requirements of § 14 UStG are most likely not met: the association is not a trader (Unternehmer), nor is a membership a performance (Leistung). Whether you have to pay a penalty depends on the wording of the section regarding the fee in the constitution.

If your membership rights have been infringed by not giving you notice of the annual general meeting, this would not give you a defence or objection against the payment of the fee. You could report this matter to the competent watchdog (Aufsichtsbehörde) under § 27(1) StBerG, though:

Aufsichtsbehörde ist die Oberfinanzdirektion oder die durch die Landesregierung bestimmte Landesfinanzbehörde. 2 Sie führt die Aufsicht über die Lohnsteuerhilfevereine, die ihren Sitz im Bezirk der Aufsichtsbehörde haben.

That is either the Oberfinanzdirektion or the Landesfinanzbehörde in the German state where the association has its statutory seat.