No delivery of my diamond ring

I sent my solitare diamond and gold ring that I paid for back to Cathy to have a look at as the diamond had a slight chip and she was going to replace it. This was on the 4th February 2016. When I emailed her, it comes back with the message that The Black Knight is no longer trading as from the 16th February. I am very concerned that I won't get my ring back.