I'm stuck with $680 in chargebacks on paypal. One gamer used a bank account to deposit funds into his account. 2-3 months later, he uses that same bank account

I'm stuck with $680 in chargebacks on paypal. One gamer used a bank account to deposit funds into his account. 2-3 months later, he uses that same bank account, then files a chargeback for $680. Even though he'd used that same bank account months earlier, on the same site without filing a chargeback somehow this time around he won the chargeback dispute. I have no idea how that is common sense possible