If your withdrawal email was changed during the hack and then re-changed after the hack, there will be traces of these actions in Fiverr and in PayPal as well.
I'm a bit confused because these statements seem contradictory :
Since your PayPal email itself is the unique identifier here, how can the same email ID lead the money into two different accounts?
From reading your other replies and the replies it seems that this was not a breach from the Fiverr side of things. Fiverr has even given you the withdrawal transaction ID. Your best bet now is to forward that transaction ID to PayPal and ask them which PayPal account that transaction relates to. It appears that things have gone wrong on the PayPal side of it, but they are refusing to own up to it.
They can do a lot, if they want. They are not impeded by logistics. The only reason they wont do something is because they don't want to do it. Don't let them hoodwink you into believing that transactions can't be reversed. They have been reversing transactions for billions of years even before the earth came into existence, for various reasons, including chargebacks, fraudulent sales, stolen credit cards etc. They can make this right if they want to.
At the same time, I do not want to give an impression that you have any legal rights here. PayPal is not registered as a full fledged bank in any country so they are not obligated to the same accountability towards their customers as a real bank is. 150$ in PayPal has the same legal validity as 150 likes on a Facebook selfie. It simply doesn't have the legal legitimacy as 'money'. Western Union and Escrow provides you those safeguards to some extent, but PayPal (and others like Skrill, Payoneer, Stripe, etc) is the wild west.
Every time something happens where PayPal is involved and things are less than ideal, I always remind myself that any resolution to the matter is contingent upon subjective things like the good will of the PayPal CS agent attending to my ticket and there is no objective protection we have as PayPal users.