Antioch Coin and Jewerly Scrapped off to lower the weight of my white gold wedding set Antioch California

I pawned my white gold wedding set when my student aid money was delayed. I kept it there for a year, paying on time the renewal interest; at the time I borrowed the money, they didn't have a policy requiring at least 24 hr. advance notice to pick up items. I showed up and gave them notice of my desire to pay the loan and claim my possessions. I returned several days later, due to their business not opening the following two days of the day I showed up. I paid with my Visa and the guy asked me to sign my ticket, I asked him for my goods, and he waved them to me from the other side of the thick window on the counter, I signed and when I got to the car, noticed that both rings had been worked on, sanding or scrapping off the gold, lowering  the weight. I have a certificate of authenticity for my wedding set, with a picture and detailed information for the rings. They are--or where--14 kt white gold with diamonds; now they show a two-tone yellowish color where they worked on my rings. Is there a possibility to legally nail this thiefs?   Please advise me of any available resources or legal venues I can use to seek justice. Thank you.