The developer does not build according to the plan

Hello,
we have a problem with our property developer.

According to the plans, we agreed with the developer that a basement window would be reduced in size and a terrace door would be installed in the kitchen. Both are recorded as such in the purchase contract.
In January, our basement was then poured and after the formwork was removed, we could see that at this point a large basement window was again planned. I already informed the seller about this 3 weeks ago (in writing and by phone). Since then, he wanted to get in touch with me. Unfortunately, I have not been able to reach him since then. Today we were at the construction site again and found that the walls of the ground floor are now being built and the recess for the terrace door in the kitchen is not present. The wall was simply continued at this point. Furthermore, we noticed that agreed relocations of other terrace doors and windows have also not been carried out.
After I looked for the very first plans of the developer that we had, I discovered that the dimensions currently used on the construction are exactly those that appear in the original plans.
What can we do now? I have pointed out the defects to the developer by email and will try again tomorrow to reach the construction manager and the seller.
The basement window and the terrace door are recorded in the purchase contract and notarized. We have also paid for these additional services. The window relocation requests have been known to the developer for a month and I approved the plans for the architect 10 days ago. So they should be available to the developer.

What rights do I have against the developer? Because of the larger basement window, which is located directly under the terrace door, an orderly entrance is only possible with considerable additional costs.

Developer or general contractor? Please check if you have used the correct term, as there are differences. From whom did you get the property?

I know, this reaction is almost a reflex whenever [Bauträger] is written. But is it really important every time and also in this case? Knowing the correct term in this case doesn’t help him at all?!

I know, this reaction is almost reflexive when the term developer is used. But is it really important every time and also in this case? Knowing the correct term in this case doesn't help him move forward?!

It is important who the client is here!

In addition, clarifying in advance saves time. Nothing is worse than having to cover all possibilities blindly in your response.

The basement window and the terrace door are recorded in the purchase contract and notarized.

That already strongly suggests a property developer. Whether that makes a difference for the problem, I don't know. Presumably, an expert won't help much either, as it is hardly a hidden defect.

Good evening,

After I looked up the very first plans from the developer that we had, I realize that the dimensions currently used in the construction are exactly those that appear in the original plans.

In general: If changes are made to the original planning, they must be approved in writing by the client on the then-valid plans. The changes must subsequently be incorporated into the execution plans and resubmitted to the client for signature. A simple release to the architect is, in my opinion, not sufficient, as he can be a possible source of error.

Have you been presented with new execution plans and approved them with your signature?

By the way, Yvonne is not wrong; the constant confusion of terms is really annoying time and again. However, the contracting party owes the contractually agreed service in both cases—whether developer or general contractor/contractor. In the case of the developer contract, however, the question arises as to how far (in time) post-contractual changes to the equipment are even possible.

Best regards from the Rhineland