I believe it's these guys
http://www.ekas.com.au/contact.html

17 calls from various numbers starting with 02 8415 85XX in four days! Very very annoying! How can I make it stop??!

keeps calling around 10pm and then hangs up when i answer. very irritating

Received many calls at different times of the day from a variety on numbers in the format 02841585XX (XX= 26/98/25/34/58/83/91/47/31/36/86/59/46/41/51/. As stated may be computer generated but the numbers MUST still be allocated to an individual or company. TELSTRA/OPTUS are the only two fixed line operators in Australia and as such these numbers MUST belong to one of their customers, if not to the carrier themselves who may be running tests. The government knows which carrier has been allocated the prefix 028415.

Numerous calls since 7 Sep 12 with no one on end of call when picking up. Probably computer initiated. Caller ID shows this basic format 08842398XX. Once home phone rings 4 times it stops and it is immediately followed by my mobile ringing in the format 02841585XX also hanging up after 4 rings. These two numbers have to be linked.