Sterns — Ring is fake

I bought a 15000 ring from sterns and they said it white gold, in less than 2 months the ring changed color, it looked like old and fake ring. I went to the store to inform them, they requested for proof of purchase. I went home and picked it up, they said they are taking it for polishing etc but after 6 months I will have to pay for that service. I said no I need my refund because that ring is fake and I can no longer keep it. They gave me customer service number and case was logged till now I have not received any update. STERNS sell FAKE jewelry.