Defective earrings not exchanged

I bought a pair of rose gold earrings at the Pandora store at JFK Airport in New York. Due to hygiene policies I could not try them on. The assistant assured me that the guarantee was valid world wide. Upon arriving back to Pretoria I wanted to wear my lovely new earrings to find that the stems were so thick that I could not get them into my ears at all! I took them to the store in Brooklyn Mall where we compared them to the other earrings and could see how thick the stems were. I was informed that they would not honour the guarantee as earrings could not be exchanged! Surely this is most unreasonable as the product is not up to standard.