They're robocalling -- using hardware and/or software that phones numbers at random.  If someone picks up, the software automatically shunts the answered call to one of their telemarketers, who then start their blurb.  Unlisted numbers can be easily contacted this way.

How do they get numbers that aren't listed

(604) 372-4404 showed up in the display as Eagle Water. Didn't answer and no message left. If they call again, I'll put them in my blocked number list.

Called and claimed someone had completed a phone survey with them and as a 'reward they were offering a 'free' water test.They scheduled a visit for less than 24 hours later. Upon investigating and deciding we didn't want or ask for any water tests the number was called back. The called number made no attempt to answer but hung up. On the second attempt the 'appointment' was successfully cancelled.