very often when exchanges or similar services have to perform some additional action regarding a transaction, they require an additional fee for such a service. I did not check the amount you sent, but I hope that the compensation for their help will not exceed the value of the transaction.
In the past, some exchanges (not all) support for deposit to a wrong chain but they charge very expensive support fee like $1000.
Example is Bittrex with support fee is $1000 (cross-chain deposit recovery) to $2500 (Unsupported ERC20 token recovery)
Bittrex deposit recovery policyFrom
Kucoin guide article, I did not see they mention about support fee so likely if possible, they don't charge any fee for case they can support their users.