There are many questions and answers about pay issues here
http://www.cab.org.nz/vat/eb/how/Pag...saboutpay.aspx on the Citizens' Advice Bureau website. As you realize, there are two parts to your problem - you are SUPPOSED to be paid at a certain rate in order to have your visa, but also, under NZ Employment Law, you are entitled to have the pay specified in your contract, and it is that aspect that the CAB are advising on. You can take action on the various lines they are suggesting to get your employer to realize that he MUST honour your contract.