I received a blank message from this number on my answering machine.  I  returned the call a couple of times the same day and once the following day.  During day time I get a busy tone and  around/after 8pm the phone rings but no one picks up.  No voicemail either.

They call constantly, several times each day, but they leave no messages. When I do answer, they will tell me nothing. From what I've read online they are some kind of debt collector but we have no outstanding debts so they clearly have the wrong person! Their last call a few minutes ago was even verbally abusive even though I had no idea what they were talking about.