Sentimental antique ring ruined

I am so heartbroken! I received a stunning antique amazonite ring (nearly 100 years old) for my 30th birthday from my boyfriend and took it in to Louie Daniele to get re-sized. A man who works there said that he would take it in but that I should read the disclaimer displayed on the reception counter and on the receipt. I told him about the ring's sentimental value and asked them to go ahead with caution and please stop if they were nervous or could see anything happening to the ring while they were working on it. My boyfriend went to pick up the ring an saw that it was completely ruined! It went from a beautiful blue-green colour to dirty brown. Louie Daniele DC still made us pay the R150 to have it resized (due to the disclaimer on the receipt), but it wasn't about the money. They are the jewellers, they should know what they're doing. If they were worried they rather should've declined working on it - especially since it had so much sentimental value. They never bothered to call to tell me about the ring or to apologise for ruining it. That ring lasted 100 years and in two days it was destroyed! I walked away paying for something that made the ring completely lose its value.