They probably didn't do any Soil Compaction before they poured the slab. Google Soil Compaction. It's very important and very technical, the testing part that is.
They are just hoping you go away. Get everybody from your salesman/woman and anybody else you deem responsible in the chain of command to help you quickly. ITS UNDER WARRANTY. Get the boss off his dead butt out to your house. Good Luck to you.
Soil compaction testing - YouTube If they took a shortcut here's your problemo!