Stolen phones may be blacklisted up to 30 days after the event. Phones used in fraudulent activity may be blacklisted up to 90 days after the event as this activity may take longer to detect.
If the phone you are using has been blacklisted, first contact the seller. If you bought the device online and the seller cannot be contacted or is uncooperative report the matter to the online marketplace directly (for example TradeMe and eBay).
You can also file a complaint with the New Zealand Police.
Only the owner who reported the phone lost or stolen can request to remove an IMEI block. If the seller was not responsible for blacklisting the phone, contact your mobile phone service provider.