Multiple Nuisance Calls

I have been receiving calls twice daily at very consistent times - between 09:00 &10:00 AWST in the morning and 14:30 to 15:30 AWST in the afternoon.

All calls appear to be coming from NSW landline numbers however it is possible they are being made or directed from another country.

I have answered a few of these calls and there is never anyone there, and on the occasions that I have returned the call the auto message says 'the number you have called is not connected'

Interestingly, when I use Skype to return the call, it converts the NSW number to one with a '64' prefix (NZ and some South Pacific Islands)

Nuisance calls received from following numbers:
(02) 8036 5459
(02) 8231 3790
(02) 8238 2542
(02) 8323 0355
(02) 8323 4357
(02) 8326 4249
(02) 8331 0529
(02) 8378 6416
(02) 8425 7131
(02) 8525 8532
(02) 8628 0583
(02) 8652 6051
(02) 8691 3876
(02) 8813 5672
(02) 8889 7262
(02) 8894 1732
(02) 8935 3493
(02) 8935 3493

Is it only a coincidence that prior to all these 'NSW' calls, I had been receiving international calls from phone numbers in Tokelau (an island in South Pacific).
Just wondered if they may somehow be related ?!?

Does anyone have any idea what these nuisance calls are about? And if it is a scam how does it work?