You should be letting zooplus know about the error. These goods do not belong to you, they belong to zooplus and are therefore not yours to sell. I have copied a bit from a BBC article here which applies to your rights:
"Items that firms send to you, but you didn't actually order are called "unsolicited goods". You're well within your rights to keep them.
You have no obligation to send them back to the company or to pay for them. If a company demands payment, that's a criminal offence.
But this doesn't apply to items sent to you by mistake (as happened to Robert); if the order was sent to you twice; or if there's extra stuff on top of what you ordered.
If a firm has left goods with you that weren't unsolicited goods, they still belong to the trader and you should try to give them back.
Firms can take you to court to recover their goods"