Neighbor has diagonally renovated the shared wall

Hello forum,

while planning our outdoor area, I just noticed that the neighbor renewed a section of a shared wall (half of the wall is on his property, the other half on mine) without asking beforehand. The wall was originally built as a shared boundary, is about 6m long but only 10cm high and 30cm wide and made of cast concrete. I would have preferred if he had asked me first, because then he could have torn down the wall and built his own boundary structure for himself. I would have then set my own edging stones and everything would have been clearly separated. For better understanding, a summary:

Two existing plots are for sale; these plots are separated by a shared wall for historical reasons
I buy the right plot, and since I did not consider the wall issue, the existing wall remains
The new neighbor buys the left plot
Half a year later, the neighbor tears down about half of the wall and recasts it in concrete

My problem now is that he built a slight curve into the wall so that it ends flush with his boundary point. As a result, I now have a curve on my property and cannot lay my paving stones neatly, cannot put a fence on the wall, etc. Of course, I will first try to talk to him, but since the neighbor will not be reachable for the next 4-6 weeks, I wanted to hear your opinion on whether this is legal and especially what can be done about the curve.

I am attaching a sketch of the situation. I hope it is clear what I mean.

If you want to pave where the arch is, then it seems like the driveway is there too. I don't find that so bad, on the contrary, it helped you create a good driveway. And you can also cut paving stones; in the end, you would have had to cut them with a straight edge as well. Sorry, I'm not made for legal matters. But I wouldn't mind, without knowing any further construction considerations from you.

Or make your curb straight and fill the edge up to the wall with gravel. I wouldn't make a fuss about it now. If the driveway is downhill, then he is the one who has to fence it in (at least in most neighborhood regulations). Then let that be his concern how he gets the fence posts fixed there.

I am attaching a sketch of the situation.

A photo would also be helpful. But I wouldn't make more of it than it is.

Well, I would bring it up. You will be living next to each other for the next few years and talking helps. In the end, the guy will do what he wants. Has the property not been built on at all yet, or did you simply overlook that he erected a wall?

There was already a wall before, it wasn’t built up in about 2 hours either.