The luster and colour would suggest dyed freshwater pearls. The size is a giveaway too. Plus, that's not a vintage clasp. It's an inexpensive modern one IMO.
They are not worth much. Probably in the <$100 range if I had to guess.
You know, if they were sold as Tahitians, you might want to seek a refund. If you got them on eBay, there is a mechanism for seeking refunds if items are not as described. Or if you bought them somewhere else, you should have recourse through consumer protection laws given that this strand is clearly not what you were told it was when you bought it.