The Postal Industry Ombudsman (PIO) investigates complaints about the provision of a postal or similar service.
The introduction of a Regular and Priority letter delivery service for consumers and an increase in the Basic Postage Rate from 70 cents to $1 came into effect on 4 January 2016. Australia Post will continue to maintain the concession stamp price at 60 cents and the seasonal greeting card rate at 65 cents. Information concerning eligibility for the concession stamp, is available here.
The Australian Competition and Consumer Commission (ACCC) has responsibility under the Competition and Consumer Act 2010 for the prices oversight of Australia Post's notified letter services [currently Australia Post's reserved ordinary letter service which includes the basic postage rate]. On 9 December 2015, ACCC released its decision to not object to Australia Post's price notification. You can read more concerning the decision here.
Price setting and the introduction of the two-speed letter service are commercial decisions for Australia Post which were considered and approved by established regulatory processes. As a matter of course, we typically do not investigate commercial/price decisions taken by Australia Post.
You can find further information concerning this matter and common complaints about Australia Post here.