Man, they have the authority to open it. There's nothing you can do about it. Them's the rules. They aren't just looking for drugs BTW. Insects, ants, plant material, parts that can be sold for profit without duty etc, in short anything.
Posting pics on social media is unprofessional. Lodge a complaint but it won't go anywhere as there's nothing directly associating it to you and you'll have to prove loss. I doubt you have 'lost' anything other than a bit of piece of mind.
In support of your anger, It is true these customs a-holes are a law unto themselves. I live here and had to ring them the other day and they are utterly diabolical to deal with. They have no idea of the law, yet they will tell you they do, and believe their own interpretation, even though that interpretation is plainly wrong.
What's worse is the threats they make, "If you are found to be in contravention of the act", and the reprisals that will follow:
They said WTTE, should I be deemed to be "In contravention of the act", regardless of whether Australian Customs deem the matter serious enough to persue in court, I was told I would be banned for life for importing any item and that any item I buy will be seized "For the rest of my life" if I am found to be "In contravention of the act." This is just plainly a damn lie from a dopey fat office worker with just a little bit too much power.
These are the people you are dealing with.
Like a vicious dog in a back yard, best not to kick the fence for shits and giggles. Just leave it alone.