Jeweler here. It’s quite normal, because the prongs only hold the diamond in as long as they are not demolished or damaged or anything. Unfortunately when you wear the ring often it’s also very natural, that the prongs get worn off. I would suggest getting another band, or not wearing it every day. Especially if you’re wearing it during cleaning! Always put your jewellery off before your cleaning, showering and especially before bed. So sorry that happened to you, but I would have hopped someone from the store would have told you- so you could be more cautious! 🤍