It doesn't sound like someone stole your work.
It sounds like you gave them your work for free.
You made a customer support ticket? Why? What is Upwork supposed to do?
If they didn't pay you for the work, then it doesn't belong to them. You can do a DMCA take-down request. But Upwork won't do that for you.
I'm sorry to learn about your experience, Ian.
I checked your account and can see that the team has continued assisting you through your support ticket. On Upwork, it is recommended to not start working on a project unless the following are met: