NOBODY demanded digging deeper or wider. The subcontractor of the general contractor apparently thought it necessary himself, and the general contractor is now charging me for it.
Have you asked what caused them to dig wider and deeper than originally ordered? As far as I understand, the first two price increases did not occur because the general contractor made a mistake. One was the price increase after the price binding expired and the other was additional civil engineering work after the geotechnical report. Especially the geotechnical report is something one should get beforehand for exactly these reasons. Accordingly, in my opinion, this is the first time you are confronted with an invoice that does not match a quote. I can understand very well that this annoys you; however, this concerns now 15m³ + 10m³ more than planned, and according to the amounts mentioned, that should be around €1500. We are also in the middle of building a house, and I can tell you that it certainly will not be the first or last time that an invoice does not turn out as expected. And I, too, often get involved in things that I think are fundamentally wrong. BUT, I do not know if I would keep chasing my principles over such a relatively small amount and thus possibly already annoy the builder. Because my experience so far has been that everything is a kind of give and take: if you "forgive" the builder a possible mistake, he will forgive you one (a planning error) and possibly even make things possible during the construction phase that were not originally planned and might have cost more. That at least is my experience so far.. :)