When you bid for projects and you get accepted to work on one of them, they take a certain percentage of the total of the project from your bank account (even before you even do the job and get any payment).

What may have happened was that one of your propositions to one of the projects got accepted and, because of that, they took the money from your account.

Check out the "fees" section of their website.

As for my recommendation, try to solve it with their support team, and then quit the website. They will do everything to try and help you, but after that, they will just turn a blind eye to you and everything will be worse.
If you can, try to work with Upwork.

In my opinion it is a scam. It happened the some hing to me. And i closed the account. But now a freelancer contacted me because he want to be refunded.