Oh my.
That's disappointing. I don't know what's next for this. If they can't blacklist the address, what should be the next step that you must be doing? to track where the amount will be sent? sorry about that mate.
Thank you for your sympathy , yes the only way is to track the transaction untill it arrive to knowing exchange or tradewebsite and find clues,
I hope that you'll track that guy as it's Tether.
I don't understand why they didn't allow you to grant the request of blacklisting the address so that hacker won't even be able to use the money that he stole. They should have taken your case not that quick but thoroughly looked at.