numerous phone calls received no one on other end when i answer it

Have started receiving up to 6-8 calls a day on my work landline from this number.  Always the same, caller hangs up after I answer.  I rang the number and was advised it was some marketing company (Agon sp?) and to call 1300 305 515.  I phoned and spoke to receptionist and was told it would take 48 hours before the calls would stop.  The calls have continued ...

Calls two or more times a day. No one on the other end. Have given up answering the calls.

Have rung 4 days straight! Really annoying me! Don't know who it is...