Settlement of additional costs for earthworks

I also fear that there is nothing more to be done here.
My lesson from similar experiences in our construction project is: No work without a prior written offer from the contracting party for the additional work to be performed. The contracting party for the additional work can be either the developer or the executing company. Usually the latter. When I agree on reduced services with a subcontractor (as happened with you), the costs are offset against the final price of the house – at least that’s what the site manager said. I hope that works too.
Of course, the entire construction process can be delayed a bit if the companies cannot start immediately after discussing the wishes but first have to prepare an offer. At least this way one is protected from extremely high, surprising bills...

No matter what happened, you have already paid without reservation. This usually means tacit acceptance in case of dispute. I am not a lawyer, but I see bad chances for you. However, the invoice does not concern you if you are not a contracting party of the TB.

Hello, I don't quite understand what is supposed to have caused the additional costs of €7000? For 1m more terrace and a parking space???? According to what the OP writes here, only topsoil (about 40cm) was removed/stripped and filled with gravel. They are building without a basement, right??? so no excavation pit and no removal of excavated material! What area are we talking about? Sorry, but something doesn't add up.... for about €7000 my civil engineer almost removes 250m² to a depth of 40cm, fills it up and compacts it... Regards Fragi

Hello Markusch,

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Previously, we were informed by a letter that the additional costs for earthworks were estimated and the exact billing would be done after the completion of the measurement. We agreed to the aforementioned additional price.
...

These two sentences are the core of the problem. If you do an exact billing after completion, you do not agree to an additional price.

Unfortunately, I also see a bleak outlook for you because you have already paid the amount. Or do you still have an outstanding amount with the main contractor? Then deduct the amount with reference to the letter!

Best regards

K.Brodbeck