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.

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!

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