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

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 ...

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

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