Building Owners' Protection Association and Expert as a Solution?

I am just wondering why the thread title was changed?

I'll briefly summarize

... that apparently the fact that something went terribly wrong is THE ONLY thing a moderator could extract as the essence from your confused mumbling. So you have obviously managed to the point that no one can make sense of your words. Sit down, take a deep breath, calm your breathing, organize your words, and follow the advice

Tell us in order...

.
I'll summarize what I hope to have understood so far:
1. It concerns an extension to a bungalow
[Question: linear extension or does it turn a rectangular bungalow into an L-shaped bungalow?]
2. The contractor was selected afterwards because they had already satisfactorily completed a similar task at your parents’ place.
3. Now you are talking about defects and some things that have gotten out of control, and a final invoice still missing. From this we can at least deduce that the construction project is stuck somewhere between "started" and "not yet successfully completed" (or "completed, but because far from defect-free not ready for acceptance"). But regarding everything else, we are standing clueless like a Martian at an intersection in Tokyo. Now pull us out of the confusion into which you have shoved us, nicely and obediently, and tell us the story of your butcher’s house from the root.

Sorry if I haven't expressed myself clearly enough.

This is not about the defects or their rectification. I don't want to go into the details now. What would that achieve? We got involved with the wrong company that advertises turnkey construction. They can do many things and do them well. But there are many things they cannot do, and then a subcontractor is brought in who is primarily cheap and accordingly works that way.

The extension (48 sqm) is basically finished, and we live in it. And I mentioned the expert in the first post to make it clear that we really tried everything to properly complete the construction project.

Unfortunately, when signing the contract nearly two years ago, we trusted too much and unfortunately signed a contract that is not valid at all. That is why the expert advised us against taking any further steps. The contractor just smiles politely and says he tricked us.

As of today, the fact is that the contractor is obviously unwilling to fix the defects, and we have not received a final invoice from him.

What I am really interested in now: as the client, do I still have any urgent tasks to complete, or should I just let everything fade away?

I wish you a nice weekend

What I am really interested in now. Do I, as a builder, still have anything urgent to take care of

Unfortunately, it is impossible to judge if you still do not tell us what it is actually about and what the current situation is. So you have the feeling that you have been taken in by some company, but: in what form this has happened shall unfortunately remain entirely your secret. So what do you want from us: that we say "oh dear, oh dear, poor little thing"???

What do you want from us then: that we say "ei, ei, heile Gänschen" ???

What is that supposed to mean?

I have already tried to put it into words twice. Do I now have to report the end of construction somewhere or can I skip that?

But I can really do without answers like that.

Sorry for bothering you. It won’t happen again!

I really can do without answers like that. Sorry for bothering you. Won't happen again!

Yes, if you keep beating around the bush, even though it's not even hot yet, THEN it is (or remains) a real nuisance. But you could also (I know, really crazy suggestion) finally explain clearly where the problem actually lies. THEN it wouldn't be pointless whining, but we could help you, and it could also benefit other readers. But only then.

Do I still have to report the completion of the construction somewhere or can I skip that?

If you have effectively accepted the new premises by moving in, of course the building authority and the household insurance must be informed. And the construction professional association will then also want to send you a questionnaire. If you really only wanted to know whether you have to continue to report completion in the same way regardless of satisfaction with the execution as if everything had gone smoothly, however, you could have left out all the fuss about parents being satisfied at the time and you now feeling cheated by the same company ! ! !

Do I still have to report the completion of construction somewhere or can I skip that.

Well, formally speaking, you are not allowed to occupy the rooms at all without a construction completion notification and approval from the office... so yes, you have to do something about it.