Refusing to pay out legitimate €7,250 winnings

I opened an account on the site and took the 100% welcome offer with a deposit of 300€, so on my account I had 300+300. I then wagered it according to the bonus terms, in accepted games, until the bonus turnover was completed. I gambled a bit more and then proceeded to withdraw my winnings: 7250€

I received an email confirming my withdrawal and later an email from the customer support congratulating me for my winnings and asking for documents the normal documents, which I sent them.

When I went to look at the situation of my withdrawal, my account had been locked by management decision as told to me in customer support chat. I was told that it was just a precaution and that I would be contacted within day or two. I waited a couple of day and sent email to the customer support about my withdrawal. The reply was that according to the terms (no explanation as to what terms) management has closed my account, confiscated my winnings and will return my deposit to me.

As far as I know, I havent broken any terms and have played according to the all the bonus rules. Seems like they allow you to lose money to the casino but as soon as you want to withdraw, it's a no-go.