Increase in earth excavation - How much is permissible?

Hi Forum!
The earthworks at our site are now completed and the final invoice has arrived.
According to the weighing certificates, the actual quantity for soil excavation and removal is about 12% above the offer/contract and for the backfilling of the working space about 50% higher! Do we have to accept this as is or are there legal limits here?

Thanks for your feedback!

It was similar for me, the question is, can they make it plausible? So why would more have to be disposed of all of a sudden, why was the workspace suddenly larger than in the planning/ the offer

No, there were no complications or anything like that. I haven't joined the discussion yet, just wanted to find out beforehand what options I have. What did you do?

So for me, it was only about the work and bringing in new soil, disposal I only did at the very end with a self-contracted civil engineer. I had already announced additional costs for the soil replacement compared to the 30cm according to the construction service description. According to the soil survey, 70cm had to be replaced, meaning I had to pay for an extra 40cm. I had calculated that and came up with a sum that was bearable. Then suddenly 1m had to be replaced after all, because a humous layer was lying unevenly in the construction area and therefore had to be completely replaced to 1m. Calculated again and gritted my teeth. The invoice was then 50% higher than the first estimate and still 25-30% higher than the second. The delivered delivery notes were not plausible and even showed more material. I then sent my calculations over and asked why it was even more expensive now. The site manager then broke down that actually not only the depth of the excavation pit had been filled, but even 20cm had been added on top. That was plausible, even though it was not clear to me beforehand and nobody said anything. With the delivery notes that still didn’t add up, but I was satisfied with the explanation that the fine grading was actually higher than the rest of the terrain at that time. So just ask and have it broken down. Of course, it’s easier if you have received the offer at the unit level beforehand and not just a lump sum.