Money Transfer and COT code

I am writing from Croatia. I have made some bitcoin trade and after many complictions was asked to open an account at Astroibank and the money was transfered into that account. When I wanted to transfer the money into my Croatian bank account I was asked for a COT code. And they are asking for a big amount of money, claiming that it cannot be deducted from the account I have with them. Is this legal? What do I do?