Been there, done that with a horse. I had purchased a horse (from a friend's grandmother). I was told she was 7-9 years old. Stupid me trusted my friend. When I got her papers-- I saw there was something missing from her age. the "1" in front of the 7. She was 17, yes 17 years old vs the 7 I was told. At that point she was at my barn, I had paid transport fees and handed over the money. I chalked it up to my own stupidity, and didn't send her back--after all the next buyer may have just sent her off to slaughter(heck, maybe the seller would have).. Atleast with me she is loved, used, and has a home.
As much as you may be upset if you were "taken" enjoy your new pet... and take it as a lesson learned for next time.