Chorus will be able decommission the copper network in areas known as "Specified Fibre Areas". There is a map available from the commerce commission https://comcom.govt.nz/regulated-industries/telecommunications/regulated-services/consumer-protections-for-copper-withdrawal/map-of-specified-fibre-areas so you can check to see if your address is within the boundary.
Some details on how the copper will be withdrawn are available on the Chorus website https://www.chorus.co.nz/copper-withdrawal/withdrawing-copper-services This also has a link through the TCF Copper withdrawal code which sets out the process in more detail.
I think I heard that two areas have been selected as part of the trial for later this year which are in the main cities but I can't find any references to them in the announcements. I expect that Chorus will start off slowly to make sure everything goes smoothly.
As mentioned in other posts, Spark is proceeding with decommissioning the NEAX equipment which provides voice services. This should be finished by 2023 according to their investor statements and is separate from the Chorus work.
So I recommend you have a look at the Commerce Commission's map and see if you are in a SPA and if not, then keep talking with your ISP about what is happening.