Is Robin not open to paying $12500 again through a separate method? If Robin is a scammer, then Upwork needs to take the loss here for not validating the money payment method.
These platforms claim to be “matchmaking services” so they can avoid this sort of issue. But if that’s really the case why do they handle billing at all? These platforms want to make sure they skim their profits from the top but when shit hits the fan they provide no protection for the freelancer.
If Robin realized he defrauded Upwork by mistake, he should just pay up. If he doesn't, then he is actually willingly defrauding upwork, who should throw the book at him.
If Robin were to pay the client outside Upwork for the $12500 charged back does the freelancer still owns Upwork 20% of the earnings? If Robin isn't paying and Upwork isn't covering the fraud is the freelancer still required to pay the 20% fees?