Is the SIM really deactivated? Do you have an account on the my vodafone website? [If you haven't already registered the phone number/SIM for an account on the Vodafone NZ website, give that a try now and see what it lists as the status of the account. Go to "My Vodafone" and look for "Not yet registered".] Some friends had some SIMs that hadn't been used for over a year, so we tried registering them on the web site. It worked and the numbers were still in the database and recognized. Adding some credit to the accounts via credit card topped them up, extended their validity and they were usable again once they returned to NZ.

One annoying thing I recall about the Vodafone website registration process is that it couldn't really handle addresses outside of NZ since it refused to proceed until you selected a city/town that it recognized. So if that's still the case, just pick your favourite.

Editing to add: this all happened/worked around 18 (?) months ago and the phones, while inactive for more than 12 months, were still able to receive the SMS sent by the system during registration.