I have never had that situation with PCB's. I have received wrong orders rarely. The resolution was either to just keep/discard or return with a prepaid shipping label. Errors happen, so I usually take the item to the shipper rather than insist the shipper pick up. IMHO, it is improper for the intended customer to be contacting you directly. I suspect WellPCB is in China and is trying to save shipping costs. That does not excuse what it did.
Have you got your boards yet? Before I did anything, I would insist on getting my order. Is the intended recipient in UK or foreign?
The simplest thing is to return the order to WellPCB at its cost. However, given the high cost of that shipping, I would be willing to ship directly to the intended customer at WellPCB's cost. I would expect well to give a significant discount up to 100% on my order, but probably not demand that.
If WellPCB is not agreeable, then I would be less agreeable too. I don't believe you own the boards, and if WellPCB arranges pickup and shipping, then you need to allow that at minimum inconvenience to yourself. Otherwise, inform WellPCB there will be a storage cost past 30 days and eventual destruction of the boards.