Right of retention and refusal to accept, whose fault?

Hello,
I have sent the message below to the floor slab company. The questions that arise for me are who is to blame that no one made me aware of the (missing) multi-utility house entry? Only the architect from abroad who did not (properly) inform himself about German laws and drew plans/ execution plans incorrectly, or also the construction company that executed it that way? As can be read below, they contacted me about mistakes, only not about what would be most important.
And what if no acceptance has taken place?
I thank you in advance for your help.

Right of retention/ claims for defects according to § 4 No. 7 VOB/B/ No acceptance

Firstly, you have until today not plausibly explained how the additional costs of about 450% for the removal of the excavated soil and construction of the driveway almost, but fortunately did not come about. If I had fallen into your trap and paid the final invoice, I would be in a considerably worse position today.
Many defects have come to light, but I will first list the worst here:

[*]In the two kitchens where the kitchen islands are located, empty conduits for the later installation of the electrical cables were forgotten.
[*]Sure, that can happen, but what are KG pipes doing for the introduction of electricity, water, and telecommunications in the house? Since 2017 at the latest, it is forbidden in Germany to install these. And don’t try to excuse yourself by saying it was drawn like that in the plan, because you pointed out some things to me that later actually caused problems, such as an extra circuit for water…

You as a company are obliged to carry out the work properly and inform customers if something is not state of the art.
I am at my wit’s end and don’t know what to do anymore. Retrofitting the multi-utility house entry is tedious, expensive, dangerous, or even impossible. In addition, the contracted prefab house company refuses to carry out further work.
I have been sleeping poorly for nights, and you have contributed a lot to that.

Now I demand with this letter that you remedy the above-mentioned defects by December 22, commission someone else to do so, or waive the final invoice as compensation for the defective work.
If this does not happen, my legal counsel will take care of it.
I am entitled to compensation as damage has occurred. Due to the defect, other work can only be carried out with delay or not at all. Furthermore, as the client, I can exercise a right of retention for progress payments in the amount of double the defect remediation costs.

Thus, you have not completed my construction site as ordered and especially not correctly.

P.S.: I do not remember any acceptance, nor that you offered me (several) appointments for it. No supervisor protocol, no witnesses, no signature… I didn’t even know when you finished/were finished.

No acceptance, no right to payment
Without acceptance, the invoice is not due. A reminder before the invoice is due is ineffective, so the customer does not fall into default. Without default, the customer also does not have to pay default interest or reimburse possible legal enforcement costs of the contractor.

If something is missing in the execution plan, why should it then be implemented? Of course, the company can kindly point it out, but as long as they stick to the plan, they are delivering the required service, right? It could be that your architect came up with something fun and fancy. Why don't you contact the architect? The German architects have appropriate insurance. If, of course, you wanted to save money with an architect from [Tadschikistan], who is not familiar with Germany, then I think "Lehrgeld" will be a term here... Just my 2 Cents

Oh dear

How can a foreign architect work in Germany? Not at all, so someone else is liable. Presumably you as the client, depending on the contract

An acceptance is not a clear declaration of intent or whatever it is called.

You may only withhold the amount it costs to fix the defects.

In the list of those responsible, the following are missing:

- The client who approved the execution plans
- The client, or their representative responsible for construction supervision

How can a foreign architect work in Germany?

I am also interested in this. For the authorities regarding the building permit, etc., we had to submit the certificate of our architect’s degree and numbers (professional chambers? registry?) everywhere. For the utilities, we had to provide proof of the qualifications of various installers and also numbers (in chambers of crafts? registry?).

If something is missing in the execution plan, why should it then be implemented? Of course, the company can kindly point it out, but as long as they stick to the plan, they are delivering the required service, right? It might be that your architect came up with something fancy and amusing. Why don’t you turn to the architect? German architects have the appropriate insurance.

If, of course, you wanted to save money with an architect from Tajikistan who is not familiar with Germany, then I think "learning the hard way" will be a relevant term here...

Just my 2 Cents

But if they had drawn a nuclear power plant in the plan, they wouldn't do it either. They have brought up a lot of things to me asking why something important is not included?