Floor-to-ceiling windows, not floor-deep

Hello,

we built a single-family house with a general contractor. Now we have the problem that the shell builder installed the roller shutter boxes too high and the windows were ordered and installed according to the plan height. As a result, the sill height for the floor window increased from the planned 1 cm to about 9 cm. The error only became apparent after the screed was laid. The defect has been reported to the general contractor. However, he refuses to address it and the shell builder also does not take any responsibility.
Does anyone have experience with this problem and can tell me how such a defect can be rectified.

Regards
EinfachIch

As it sounds with a good lawyer :D Otherwise there's only one option... tear it out and redo it.