receiving constant calls from this number but no messages are left and cannot ring back as line is constantly engaged. Calls are coming in sometimes up to 4 times per day.

I am also getting constant calls from this number on my mobile and can't return the call. Don't know who it is.

Some guy trying to sell phone deals.  Seems shoddy, not very professional.  I did my usual thing... told him that my hourly rate was $69.30 and I'd be happy to chat with him once he agreed to my charges.  I'm not sure if it helps, but it always makes me laugh!  Try it!