You can contact the service provider, and the escrow agent to request a refund, but beyond that there is likely nothing that can be done. If you have lost a substantial amount of money, you could file reports with your local law enforcement agency, but understand that there is almost no chance they will be able to help you recover the funds.
Bitcoin transactions are not reversible, once confirmed several blocks deep in the blockchain history, the chance of that transaction being removed or replaced is basically zero. The only way those funds can be returned, is if the person who now controls them decides to send a transaction paying you back.
Sorry for your loss here, it is unfortunate to hear that even after employing an escrow agent, your trade did not go as planned.