My ring is black and one stone fell off

So my fiance bought an engagement ring at American Swiss The Glen Shopping Centre. Within a week it was turning black and brown and the stones where black did not look silver anymore. Took to it American Swiss Greenstone and the ladies there told me they will clean it with their solution, that did not help i eventually got tired of taking trips to the stores for cleaning. Until in February when stone fell off from the side I eventually got @#&amp