they can issue a “call tag” for it, and you can schedule a pick up at your office or whatever. Most places that screw up like that are happy to handle it that way. PSA is usually real good about customer service.
Once the package is picked up they then release / send the correct item. This is done often in the computer industry to minimize down time. Otherwise your down time is doubled e.g. They receive your ammo, process it then send out the correct ammo order.
I have done this on many things other than computer related items. It just takes a little bit of coordination on the offending businesses part.
This is a little different but I ordered a PTAC BCG from PSA and wanted the higher end premium BCG. I called them and the exchanged it before it shipped and I had it two days later. Their customer service is pretty helpful. Just be prepared to wait on hold for a little bit.