The most accurate answer you can get will be from past invoices or IT help, especially as you might be dealing with a reseller that will not show up with the below methods.
Find your domain registrar:
Most domain registries have a WHOIS database which will normally show the domain registrar and contact information for the domain. Generally, the registrar and technical contacts are useful for getting help with your domain name. Web administrators will often put their details on the technical contact in case you need advice.
Here are some useful tools for viewing the WHOIS data:
.nz domain WHOIS lookup tool: https://dnc.org.nz/whois/whois-lookup/
International (gTLD) domain WHOIS lookup tool: https://lookup.icann.org/en
On Mac or Linux computers, you can run a command like whois myhost.nz from the Terminal application.
Find your hosting provider:
You can enter your domain name in a the following tool and select "DNS Lookup" to find the IP addresses of the servers running your website: https://mxtoolbox.com/SuperTool.aspx#
Underneath the IP address you will see the name of the company this IP address has been allocated to. For MyHost, this is our sister company "SiteTech Solutions Limited".
You can also enter this IP address and select "Reverse Lookup" to see the hostname for the server. For example, if you are hosted on MyHost you will see something like "rahotu.myhost.nz":
