Bershka Necklace Discoloration, and Skin Irritation Problem

I purchased a necklace from Bershka, and unfortunately, it has undergone some changes. It has darkened, lost its original color, and caused redness and swelling in the area where I wore it. Even though I frequently shop with this brand and highly recommend their products, I strongly advise against purchasing jewelry. I experienced a significant impact on my overall well-being. I have a complaint.