Orthodontist out of business. Who to contact?

I completed two years of Invisalign treatment last July and my Orthodontist gave me a retainer. in October, the retainer broke while it was in my hand. Nothing really happened to cause it to break. I called my orthodontist and found out. They are no longer in business. I need a replacement retainer and called Invisalign customer service speaking to someone twice, who said I would get a call back. It’s been two weeks now since I talked to the last person and still haven’t gotten a call back. I just want a replacement retainer. Is this reasonable? Anybody have experience with Invisalign backing up their product?