hands,

You probably should seek the advice of a lawyer and check to see if the
builder is still in business.
Your post is a bit confusing since you claim the house is not able to
bear it's specified load but you prove this with soil tests. I suspect that
you mean that the foundation has problems. As others have said a house with
a bad foundation has little value. You'll need to fix this. With luck the
builder will pay.

Dave M.