Hello Zak
If there is a prefix hijack, then you need to first figure from where the route is originating and reach out to that ISP or your local ISP to inform about the same. You dont really need to reach out to APNIC. Its the ISP's who have to deal with the prefix hijacks. If a prefix x.x.x.x/y is being learnt from ISP A, notify ISP A about that prefix. ISP A will then figure out which of their customer is advertising that hijacked prefix and based on that they will ask them to stop that prefix or the ISP themselves can block that prefix.
Hope this helps.
Regards
Vinit
Thanks
--Vinit