How to reduce PayPal fraud payments?

Hello everybody.
In short we get payments from stolen debit/credit cards for purchasing our online services. When the card holder understands what is going on PayPal puts the money on hold and we don't have any chance.
Started to refund the payments and even after refund (which even does 5% loss) we sometimes get chargeback fees of $ 20!
Can somebody give some ideas to prevent this. The ratio of real/fraud payments is like 50/50 which reduces our profits a lot…
Any ideas?

Thanks