A company sent goods I never ordered and now demands payment

You are generally not obliged to pay for goods you did not order. The Fair Trading Act 1986 deals with unsolicited goods and provides that a person who receives goods they did not request is not liable to pay for them, and the sender cannot demand payment or threaten action as though there were a contract. You are not required to return the goods at your own cost, although you should keep them safe and available for collection for a reasonable period. Send a short written response saying you did not order the goods, you are not liable and the goods are available for collection at the sender's cost. Keep the parcel and all correspondence. Demanding payment for unsolicited goods can itself be a breach, so a complaint to the Commerce Commission is appropriate if the demands continue.