Probably Mobile Testers. They spoof numbers and then ring you to see if the number is working then they farm the numbers out to solar panel companies and electricity companies so you get a million calls from India. Cant someone do something about this?
I wish apple would let you ban a range of numbers - I do not answer any 0489 numbers as they are all spammers.

Didn't answer. No message. Spam dialler pattern.

rang for two rings and stopped, came right after another random number