My advice would be to not use them for divination any more. Either cleanse and discard them, or use them individually as meditation focal points or as amulets. Take the time to create a set of your own, ideally using wood, although you could use ceramic, clay, stone, or even cardboard. Consecrate the set before using it and carry it with you or keep it under your pillow for a few weeks until it absorbs your aura. A set you make yourself always works better than a manufactured set.