PP is well known in my experience to just throw something in the box and ship it, if they can't find the proper item in the warehouse. Like getting windshield washer hose when you ordered injector return line.
The proper way to deal with them is threaten to charge-back the credit card unless they send you a prepaid UPS return label. The customer should not pay to return items PP sent by mistake.
Typically businesses hate the idea of a credit card charge-back, because it is something of a strike against their relationship with the card companies. It makes doing business much more expensive for them if they get excessive charge-backs. So it is usually a large incentive for them to do the right thing if you just mention you are considering a charge-back.
I deal with PP only if they have something I can't get from WorldPac or reasonably priced from the d-d-d-stealer.
Ken300D