This is a scam bud, a very common one at that, I remember that this scam tactics reigned well around 2017 - 2020 and alot of persons fell victim to it.

What you have to know is that your account isn't charged with any bitcoin, not even 1 or half of it, your account balance is zero, the scammer just made things look real to you for a reason no other than to scam you, the site itself is a scam, owned and managed by scammers, so don't pay them any dime, you will only lose your money.

Think about this this way, there is 12 bitcoins on your account which was given to you by them, but amazingly, they need you to pay $1000 before they can allow you withdraw the money, 12 bitcoin itself is money and worth much more than $1000, why don't they simply take the $1000 they need from the 12 bitcoin and allow you withdraw the remaining balance in peace? 😁

This is an old scam tactics, don't fall victim to it, and good thing you even asked this here before taking any action.