Crown diamonds service for repair is a rip off, I waited for someone to call back and they never called Fullerton, California

I sent my fiance ring in to have the diamond replaced which fell off, I have a warranty that says it will replace it. OK first of all the sterling ring turned dull and I was told that it showed someone made marks on the ring or removed. Why would I leave behind evidence with marks on the ring? I sent the ring over a month ago and waited for a phone call, 4 weeks went by so I called for the service department, I was told they would call back but they didnt...I kept calling until I spoke to someone and even asked for a  manager which I was told that didnt have one, what a joke they are. When I did talk to someone they said that I would have to pay 25% of the cost of the ring which I paid $4,000.00 for to replace...I dont think so I paid the ring off I dont need to pay for the difference especially if its a 4k ring for that price you would think it would not Fall OFF!!!