Foundation positioned incorrectly, what to do?

Since there still seem to be misunderstandings in parts:

No :)

I would get the expert/appraiser to see what he thinks about it. You don't have one, do you?

Applies to the foundation too!

Since there still seem to be some misunderstandings: The slab has not yet been poured. [...] This is "only" about the strip foundations under the slab or the formwork blocks. [...] What would a demolition of the same approximately cost?

So with the "not yet poured" slab you mean the planar part of the slab, but the strips already exist? Apart from the fact that they are probably incorrectly placed now (I am not assuming a 3m structural grid of your house layout), I find the idea, to put it mildly, "unusual" to create the strip thickening and the planar part of the slab in separate construction phases. What the formwork blocks have to do with the whole story is still unclear to me. Maybe you should illustrate this nonsense first before we continue to talk about the sauce :)

I find the idea, to put the strip-like thickened parts and the flat part of the slab in separate construction phases, to be, to put it mildly, "unusual".

No, you can probably do it that way if it’s a slab that is not designed as a load-bearing structure. It was the same with me. According to other experts (different from Meiningen), it’s a cheap construction method and should actually no longer be done, but it is technically OK.

No, you can probably do it that way, if it is a BP that is not designed as a supporting structure. It was the same for me. According to other experts (besides Meininger), it is a cheap construction method and should actually no longer be done, but it is technically OK.

Ouch. Qualitatively, I would fully agree with the "cheap" there, but price-wise I can’t imagine much benefit. And from the stated condition it unfortunately follows that the strips must lie strictly below the loads. Even more ouch ;-)

As I have always liked to say, the language of the engineer is the plan. Where are the plans of the planned house, where are the plans of the current state, where are the plans of the proposed changes with the corresponding new reinforcement drawing and checked static calculations. Until then, construction stop. Of course, any client can impose a construction stop. Here, it is more than advisable.

honestly, when the string line is set up, can't you see a deviation of 3 m?

Are there really no pictures of this nonsense? That is the least you can do to secure evidence.