I gave you all my exchanges id. Who but the owner knows about this? You just found a reason not to give this money away.
We could've either issued a refund to an address you sent us deposit from or proceed with your exchange — what you want us to do is to send 3 BTC to an unknown address by providing us with an Exchange ID.
We can't send 3 BTC to a 3rd party address without being absolute certainty in the fact that we are talking to the owner of the funds.