There are already many complaints against this exchange, and yet you still sent such a large amount of funds, which is really disappointing. When using this type of exchange, you should always send small amounts of funds. I saw on the bestchange review page that they are asking you to do additional kyc verification and they got a link to an unlawful source of your funds! Actually these are their regular excuses to keep customers' big funds.
Even if the source of the funds is suspicious, the platform has no right to retain them. Legally, the funds must be returned to the same address from which it came (this is why it's dangerous to deposit directly as a withdraw from another platform, should always use personal addresses), or the authorities must be notified to open an investigation about the user and the suspicious funds.