You moved in before an Occupancy Permit was issued? According to the Building Commission that is illegal:
“Section 39 of the Building Act 1993 requires that – where a building permit states that an occupancy permit is required for the building, it is an offence for a person to occupy the building unless the occupancy permit has been issued. Therefore, it is the owner’s responsibility to ensure that the occupancy permit has been issued.”
Are you sure of the developer’s story? The Occupancy Permit should have been checked as part of the purchase process.