Sorry, don't mean to be rude, but your story doesn't track for many reasons. First, PIX keys are associated to formal bank accounts. If what you described happend, that account was blocked by the bank likely within the hour after the 'robbery'. And "stealing" accounts from other people in a way that allows you to withdraw cash from is exceedingly difficult and uncommon.
Furthermore, it might have been possible in early days of pix, but it's been some time now (maybe from the start? Making your story impossible) that Pix has a 'undo' feature that the sender can do on their bank app or ATM even; similar to the 'block this credit transaction' from a credit card.
> With Pix, as I understand it, nobody feels responsible for it and the money is gone.
Incorrect, see above. Are you confusing PIX for some kind of crypto transfer?