Calls then hangs up without saying anything

I rang this number back and they told me its a online bookmaker from Darwin!  Don't know how they got our number!?! They were going to remove our number from their list but lo and behold a couple of hours later we got another call looking for someone.  I asked why they kept calling and they said it was about our online account...but we don't have one!!!!

Same here Lachlan, called yesterday 20th April and then today (just now) 21st April.