It is a really 騙局

Firstly, you think you had already got the $6000. However, you didn't. In fact, if you re-fund the money to their account, you will get information soon that those $6000 canceled or the account has not enough money. They have at least one month to do it.

So anyone if they want to you re-fund any money, the only thing you need do is rejected it. Tell them pay exactly money to you and you don't do any re-fund.