Sadly, I don't think you'll get far.

A chargeback is done from the buyer's bank and it seems the banks don't don't care what PayPal say about the case.  I've had a number of chargebacks now and nothing ever changes no matter what I can give PayPal as proof.

They can't even reveal which bank it is so I can chase it up directly with the buyer's bank.

Sometimes, it is actually the bank calling the buyer and saying, "We noticed this unusual transaction, did you know about it?" and the buyer will just agree to it being suspicious so the bank will lodge a dispute and get their money back, and cause a great deal of grief for an innocent seller and not care about it when we contact them asking them to reverse it.