While it's not foundation related, I have an experience where I had to deal with my builder about a problem....
I'll try to keep it concise -
We built our house in 2003. We have a finished basement, a main floor, and a second story. Right away we could tell there was an issue with the heating/cooling. The airflow was too strong in the basement and very weak in the second story. The second story was always super cold (even though heat rises) and the basement was like an oven. Things were just totally backwards.
We contacted the builder and they sent out their heating/cooling contractor (several visits). He'd turn the heat/AC on & off, walk around, stick a thermometer in the vents, and basically tell us everything was OK and that we needed to close the vents in the basement and the main level to push the airflow the second story. He basically dismissed us every time.
I got more and more angry because I knew something was wrong. So, I took things in my own hands and called two separate independent heating/cooling contractors and paid them to inspect our system. They both did full inspections and spent ALOT of time making notes on what they found. They each charged under $100.
The inspections found that the heat exchanger was bad and no dampers were installed so the airflow could be adjusted.
I wrote a letter to my builder (sent certified mail) about the inspections and the findings. Guess what? My builder FINALLY fixed the problem. They sent a different heating/cooling contractor (not the one that kept coming to my house and saying everything was OK) and the replaced the heat exchanger and installed dampers at no cost to me. They didn't reimburse the cost of having the two independent contractors do their inspections but that was OK because it got the problem fixed.
Good luck with your builder. Be strong!