It's a test call. They call to see if the number is live and in use. When you answer and they know there's a person on the other end and not a machine or the number is disconnected, they sell the number on to spammers.

i ignored the call. Rang back later and was told that this number was not listed. They did ring again and when asked why i couldn't return the call, the person hung up

And they've started again, new year, new harassment!! It was nice and quiet from Christmas till about Monday this week, now they're back. This number rang my landline, I just picked up the phone and dropped it back in it's cradle. Just b**** off losers!!

I rang once and got disconnected