Unless they are now having to work 40 hours of overtime to cover your work I would not think this is a problem.
if they are eliminating your position, why would they give your hours to anyone? that wouldn t save them any money - if there wasn t enough work to justify keeping you, there would be no work that required anyone else to get more hours
I m afraid that I cannot answer for New Zealand law (your answer has come up on the UK site) but over here that would be perfectly legal and in fact is what always happens.