Hellnick: always CALL PayPal. They are far more helpful by phone, at least in the US. I have conviced them to reverse prior bad decisions on more than one occasion. Be firm but polite with them. If you funded your payment with your credit card, you can also do chargeback with them. Most cc companies will do a chargeback when pp is uncooperative, often without question.
PayPal require that you raise a complaint within 45 days of payment - there was a 3 or 4 week delay in Audiothinker sending the item and then I've spent weeks hassling the delivery company and then trying to get a coherent response from Audiothinker, so I'm outside the 45 day limit. Good point on the credit card - the Paypal payment was linked to my credit card so I'll give that a go.
Cheers for the advice.