Refusing to accept delivery will likely result in a "Non delivery" and may just go back with the courier who will throw it back in a corner in the depot. Best you notify the sender of your intentions so they can request a RTS once it scans back as a non delivery.
Ok good, I already a while ago sent the company an email asking them to call me (they are closed at this hour) to clear up the confusion and that I would refuse delivery and have it sent back to them. I just wasn't sure it was possible to do this with an NZ post courier since I've never had to do it before. Now I just have to make sure the spouse doesn't accidentally sign for it as we are expecting a different parcel as well!
Do I just explain to the courier I want it returned to sender?