In NZ you sign up with an ISP, but your local connection is usually handled by the same physical equipment (DSLAM for ADSL, etc) which is owned by a single network provider.
I’m not sure what the incentives are for an ISP to try to get the provider to fix issues, or even if they would e.g. https://company.chorus.co.nz/what-we-do is notoriously bad for service and the copper network is being deprecated. Locally https://www.enable.net.nz/about-enable/ are doing a good job of service, because they are well subsidised by the government and seem to be effectively operated.
I’m not sure what the incentives are for an ISP to try to get the provider to fix issues, or even if they would e.g. https://company.chorus.co.nz/what-we-do is notoriously bad for service and the copper network is being deprecated. Locally https://www.enable.net.nz/about-enable/ are doing a good job of service, because they are well subsidised by the government and seem to be effectively operated.