Controlled Delivery of 100 Grams of MDMA, Followed by a Police Raid

My question involves criminal law for the state of: Australia

I have just had a controlled delivery happen at my home of residents where I had a friend who shares the house with me accept a package on my behalf (he signed).

I had gotten home an hour later after my lunch to find out that theirs a unknown package for me in my address and name (I wasn't expecting anything) I didn't open it I wrote RTS on it and 5 minutes later police come and raid my house and now I am being charged for possession on 100grams of MDMA which I didn't sign for or take possession of I clearly wrote RTS because I didn't know this sender he was from Germany.

Does this seem right, how can I be charged for this?

This forum deals with US law.

From a law enforcement standpoint, at some point in the transit of a package from a drug trafficker to you, they identified the contents of the package. They then did the controlled delivery, and somebody in your home signed for the package. Given that drug dealers are not in the business of sending out free samples to international clients, from a law enforcement standpoint, the question is much less whether somebody ordered a shipment of drugs to be delivered under your name to your home, and much more whether you can identify somebody else who could have placed the order under your name and expected to receive the package before you opened it, discovered drugs inside and called the police.

100 grams of MDMA.... roughly $20K AUD, street value?

Not sure what the street value is.

I just don't get how I can get charged for this mysterious package that I NEVER wanted delivered to my house.

My room mate has signed for this package and put it inside, I have gotten home and didn't know what it was so I put "return to sender" on it and now i'm being charged?

TL;DR I didn't sign for package. I didn't take possession of package. I didn't open package. I wrote return to sender on package as I had no idea what it was.

If you can get the police and prosecutor to believe that, you'll be in good shape.

have just heard from the police and they don't have enough evidence to prosecute me so I am free to go. Thanks a lot for helping me out.