Legal action is pointless, by the way, if you want to get things done.
That is true if you want to fight for something yourself, like a building permit, an exemption, a deviation, or, as at the beginning here, the possibility of a free withdrawal from the purchase contract or even the claim for damages due to unforeseeable additional costs caused by planning errors.
Now, however, the wrongdoers (personally, of course, others, but all employees of the municipality always act on behalf of the mayor) are even threatening coercive measures, against which it is worth defending oneself. And since the town hall apparently holds the view that the individual citizen can do nothing to me, a professional should be installed in the background who explains the legal options from both sides and, if necessary, prevents the worst. There are also associations that inform a builder about his rights and obligations without promoting an escalation.