Diamonds falling out

My husband purchased a tanzanite and diamond ring for our 5th wedding anniversary and within a year it lost one of its diamonds. We took it to Browns and complained about the poor quality and got told it’s my fault as I wear the ring too often. This a ring I wear a couple times a week. We paid to get it fixed and for a new diamond and were assured the clasps were all checked. 6 months later the same stone fell out! Again they claim no responsibility! Now I’m faced with having to pay for another diamond for a ring I can’t wear as its guaranteed to fall out again and I can’t afford to keep replacing it every year. WhT are my rights here?