Sorry to hear that. Please try to contact the man who hired for your project. If he/she doesn't reply then you can dispute. Please have a look details here: https://support.upwork.com/hc/en-us/sections/202260418-Disputes?flash_digest=425ed0ac4c431ee4f279022...
You can see here Hourly protection: https://youtu.be/YQJgkqPpLYM
Here you can find fixed price protection also: https://youtu.be/RhmRk-ZuUT0
If you need any assist further feel free to ask.
I'm sorry to hear you had an unfortunate experience on this contract, Judd. I checked the contract and can see that your first two milestones has already been paid, while the third milestone remain unfunded. You will not be able to file a dispute on an unfunded milestone, but I'll go ahead and double check with the team what can be done about this contract.
You've lost your money. Already the response is you have to fund before they will do anything. I lost $500 recently as they pay out - even if you complain to the customer service beforehand - unless you specifically challenge on the project timesheet. They automatically "assume" you are satisifed if you don't do that within a short timefame - why? Because they want their cut!