I was under the impression the pharmaceutical benefits scheme only lists certain quantities of meds to be covered, so chemists only sell that quantity. Ie I needed a steroid cream but I had to buy two huge tubes because that's the only way they came as a subsidized product. I prob could have sourced a smaller tube but it would have cost a lot more. Basically I'm saying the meds were in date when you bought them, they prob only come in that size and I would think its unlikely a chemist would accept a return.

Hope this helps