Fixed term tenancies, once expired become periodic tenancies. The landlord may then kick you out at any time, with 21 days notice. So they may plan to get new tenants and then serve you notice to leave. If you haven't been told to leave at the end of the tenancy then nothing has been done incorrectly here, and you don't have to leave until you get told to.

That being said, the landlord in the current situation has no requirement to give you another fixed term agreement, and if they do - they may increase the rent. As they notified you (in writing I assume?) 60 days ago of an increase to $460, this will now be your rent amount.

You may wish to read this in regards to the rent increase:

https://www.tenancy.govt.nz/rent-bond-and-bills/rent/increasing-rent/