Pulsation/Vibration in Steering Wheel?

I recently had my ball joint replaced by a local shop. On the way home from the shop, my wheel starting shaking and wobbling once I got up around 50MPH. I then stopped and something is smoking from the front end. I'm pretty sure they replaced it wrong, so I was wondering what can I lawfully do. They said that their shop is a NAPA Autocare Center and their repairs are covered under a 2 year 24,000 mile warranty. I called them and left a voicemail because the repair was done on Friday and they were closed by the time I called. If I take my Jeep back in are they required by law to repair it for free, etc.? Thanks for any response