If you've ever ordered anything online and had to provide your number - I'm a prepaid phone so it's not listed anywhere - those lists are sometimes on-sold to marketing companies etc.
The 'do not call' register/list apparently expires after a few years

Strange call I answered & it was a recorded message in chinese that repeated it self several times. I've had my number for over 20 years so I know nothing or anyone that would call me speaking chinese I'm Aussie born & bred for over 150 years.