Diamonds falling off

On two occasions my husband had purchased me gifts from Browns once my wedding ring and second a wedding band. And on both rings purchased my diamonds fell off. On the first occasion the diamond fell off and Browns took the ring and tightened the claws , lucky the diamond fell in my car and I was able to spot it. This happened within few months of getting married and I was utterly disgusted. My husband convinced me at this time things like this happen and I should forget it. He then went back to Browns and purchased a Christmas gift I 2014 December despite my greater efforts telling him not to. And 4 months later the diamond falls off again. This time I am appalled at the disgrace of wearing a ring and my personal assisting alerting me my diamonds are missing. Further to this my wedding ring moved from a gold colour to a dirty brown colour and the explanation was it needs to be rhodium plated yearly. I have other rings from different jewelry stores and non changed colour. I own diamond earrings from American swiss, an engagement ring from American Swiss a diamond ring from NWJ jewllers just to name a few but never experienced such poor workmanship and falling diamonds. disgusted