4 years after construction, the office also demands land acquisition tax on the house

Why does the [FA] actually have the contract on file?

Why does the tax office actually have the contract on file?

Because the notary is obliged to pass it on - because of the real estate transfer tax.

Does everything automatically go from the notary to the tax office? They also immediately check where the money is coming from.

There is only one sensible piece of advice here: Go to a tax advisor, preferably one who specializes in [Grunderwerbsteuer]. This is not necessarily the everyday business of a "Wald und Wiesen" tax advisor!

Why does the tax office actually have the contract on file?

In the course of the land purchase contract, it goes to the tax office. They determine the tax and issue the certificate of clearance after payment. Without that, the notary cannot proceed with the purchase. The present case is, in my opinion, the prime example of a tied transaction. There is nothing to discuss. The developer contract is also not available, so no reclaiming VAT. The letter now present extends the deadline; delaying over the turn of the year also does not help. Have it checked externally. Of course, it doesn't cost 10k like our forum sovereign citizen claims. But the chances are low, one just has to say that.

As harsh as it sounds, I would probably bite the bullet and pay the tax. At first, it feels terrible, completely understandable. But I see little chance to wiggle out of it if it was clearly a tied deal. For the squabbling with the tax office, hiring a specialist lawyer or tax advisor now... you don't have to throw good money after bad. Just my opinion, not legal advice.