Beyond telling Customer Support that you’re unhappy, there’s nothing more you can do. You can’t review the Seller when a cancellation has been initiated (for good reason). Also, you’ve got your money back, and are now free to source an alternative supplier to get the work done. I don’t know what more you think Customer Support will be able to do for you?
Who knows? Perhaps something came up in his or her life? A family emergency? Sudden illness? We’re all freelancers here, this isn’t Amazon. You’re dealing with real people, and sometimes things happen. Maybe the seller felt they were in over their head and didn’t want to send you shabby work. I’d actually argue that they did the right thing by cancelling, as opposed to sending you sub-quality work.
I do understand your frustration about the time it’s taken, and yes your seller could and should have been more forthcoming with communication. But this is the risk you take dealing with freelancers. If your deadline was that tight, you could have declined the request for extra time, forcing the seller to make a cancellation decision 2 days earlier.
I’m sorry that this has put your project in jeopardy, but I don’t know what more you’re looking for at this point?