Do you think I should take legal action?

I had gone to the mall with my brother and was about to leave till i found out I didn't know where my new apple IPhone4 was. We used my brother's phone to call it and an associate from Vans answered, (Vans is a store in the mall) saying that they had the phone and had it stored away. So me and my brother ran back to the store minutes later, only to find out another sales associate gave it away to another person without asking for proof that it was indeed theirs. To my complete dismay, I called it, and the theifs turned it off. I can't track it and my dad took it off our plan, but that doesn't change the fact that it was 800 dollars out of my pocket, and Vans gave it away. They say they're not responsible but I beg to differ. Any opinions?