Unfortunately, there is no way you are getting it back and if anyone is promising you that, just be sure they are out to scam you of the one you have left. The only way you are getting it back is if the site decide to own up and be responsible for their inefficiencies and decides to compensate you for your loss, there is hardly anything you can do about it no matter how you try.

But the confusing part which I am yet to phantom is why would you keep such an amount on another person's platform even in the real world, rich people don't keep majority of their funds in the bank rather they invest it in assets in their name which makes it more secure. And bitcoin has made this more cheaper and easier for you to do. Just by downloading a wallet where you have the private key and you are safe but people still fall for this despite the abundance of this warning every where.