Construction company halts work despite overpayment

: This is not stated in our scope of construction services.

This is not the scope of construction services, this is the contract.
You also need to have the scope of services. The scope of construction services. Where is it? The agent has one on his homepage. That should be it. And it states what is not included in the fixed price. Or rather: what is not included must be borne by the client.

Yes, then please upload all the contracts here, so one can get a better idea. The construction service description is explicitly mentioned under 2.3, it is part of the contract.

The fact is that there is a signed construction contract that both parties must adhere to. And there is nothing about additional costs due to structural reasons.

Annex 1 includes our additional requests. By the way, the disposal of the soil was billed separately.

I have to disagree. Compliance with structural engineering requirements is a building regulation obligation. The contract states: "Not included in the scope of services are cost-incurring requirements of the building authority [..] or comparable regulations [..]".
So, you pay. Quite simple.

Nevertheless, the entire Annex 1 would be very important to see. Also the construction performance description, which is explicitly mentioned in §2.3.

Annex 1 includes our additional requests. By the way, the disposal of the soil was billed separately.

No, the additional requests are only part of the construction performance description, namely a separate subsection.
It is normal that the disposal of the soil is billed separately. Show us the excerpt for the earthworks if the whole construction performance description is too much to post for you.

The contract states only matter-of-factly that the house will be built when "the building site is ready for construction." That would not include earthworks.

That the earthworks were charged separately was okay. Just not the amount that was ultimately hauled away. That was over 1100 tons. And now the earth is missing for backfilling. So clearly too much was hauled away and charged to me.