Please forgive me, but I just don’t get it right now... What are the conditions to benefit from the funding? Which date counts there, or in what order are the 10000 HP application for funding and the conclusion of the house construction contract supposed to be made? That is not clear to me, nor what “all orders for the 10000 HP have been placed” means. How can I have placed an order when applying for funding? Or am I missing something [emoji51] Otherwise, at least with BAFA (funding for heat pumps), it goes like this: first submit the funding application, then commission the heating installer/sign the house construction contract, the order date counts. Tenders (if applicable) can be done beforehand, but the commissioning/contract signature only AFTER the funding application. Otherwise, you will probably get nothing.
I am not a lawyer, whether a lawsuit makes sense should be assessed by one. My gut feeling, that of a layperson, tells me that the order was not followed (you as builders first signed the contract and thus made a declaration of intent, then applied for the funding, which IMHO was a mistake.) But as I said, whether your declaration of intent is decisive for the exclusion date of the funding (the reason for rejection suggests that) or the conclusion by countersigning by the house building company, better ask a lawyer.
Even if it doesn’t help you, maybe for readers: count on the money you definitely have, not on funding that has not yet been approved. As far as I know, the 10000 HP is also limited, i.e. if the pot is empty, you get nothing. For that reason alone, better only count on what you have and if in doubt be glad that you got a portion back through funding.
Can you also say something about the house building company promising you the funding? Is that in the house construction contract or how is it worded? Possibly there are claims for damages -> ask lawyers.
However, I would ask myself how the house building company can give you such a promise about funding (and thus other people’s money). It must be applied for AND approved... the company has no influence on that, right? Were you perhaps too gullible there?