I'm sorry you feel duped
I think many of us "toy breed" lovers bought a Yorkie/Maltese/Chihuahua hoping he or she would stay small.
My Sammie is 5 months and just under 3 pounds....but in one year, he may grow to be 10 pounds. Who knows??!?!
All I can go by is his parents....mom 6 pounds, dad 3 pounds. That is probably your best bet. Also, when people buy from a breeder, ask to see the parents so you can see coloring, body style, etc.
It's a shame many people use the teacup term to appeal to the buyer and sky rocket the price.
Talk to the person you bought your puppy from because there are many people who DO GAURENTEE THE SIZE!!! Believe it not, I know several people who have been breeding since early 1980s ....and they have quality smaller Yorkies that through many years (avoiding inbreeding) have generations and generations of proof that their puppies will be small
Good luck