Where did you get 600 GB per day? That only would’ve cost $8.40 per day. It looks like it was actually 25 TB per day which is over 40x what you said.

From the article:

This was about AU$350 a day for a month… priced at AU$0.014 per GB

A company could not stay in business if every one of their “unlimited 1 Gbps” customers for €40 per month actually used that bandwidth.