I think it'll be as close to impossible to have them back unless you hire those people who caught the bitfinex hackers.
Do you think that is possible to hire the U.S. Federal Police (FBI) to deal with a private case in which someone was left without $6300 in cryptocurrency? I'm sure they don't even blink at such things, they are only interested in cases worth millions, so the only thing the OP can hope for is that his case it is part of a big scam and that the perpetrators will one day be caught.
Thanks for the correction. I missed that one zero. OP has lost a huge amount of money $6300 is not chicken change no surprise he wants his money back at all cost.
You're welcome. $900 is not a small amount in some countries, but the OP does not seem to be from such a country when it can afford such gambling with thousands of $. His wishes and reality are unfortunately very far from each other, but he can always hope - at least it's free.