I've had a similar issue to the OP. I ordered computer case HDD mounting parts to the tune of about AUD$80. Here's my advice and story...
Be selective about where you get your tracking information from. If you use the tracking links that AliExpress provide, you will see the tracking information from the China Post point of view. As far as the sellers and AliExpress are concerned, once the package arrives in Australia, AliExpress assume it was handed over to Australia Post for final delivery and they declare it as delivered. They do not appear to track in the destination country - at least not with cheap/free shipping options to Australia.
When I had a similar issue, I managed to find a 3rd party package tracking site that had more detailed tracking information, including the tracking number that Australia Post assigned for local delivery. I used that information to contact Australia Post about the missing package and they managed to track it as far as the local delivery centre and then the trail stopped. Australia Post got the delivery centre to look for the missing package, but a few days later they reported back, saying that they can not find the package and that it is now considered lost. They also suggested that I do not waste time with AliExpress and request a charge back from my credit card before the time limit for that expires.
I thought that I would give AliExpress a chance to do the right and jumped through the various hoops, roadblocks and obstacles that they threw up. This included having to open a dispute using a different topic to be even able to get through to someone. After a few weeks of going back and forth with the seller and AliExpress dispute team, including sending them links and screen shots of Australia Post declaring the package lost, I was getting nowhere. The AliExpress support staff insisted that it was delivered and gave me advice ranging from waiting longer to asking neighbours if they had my package. At that point I told them that there was clearly enough evidence supplied to prove the package was never delivered and that they could seek compensation from their postal service as per advice from Australia Post. I also told them that I was going to contact my credit card issuer, ask for a charge back and provide the credit card issuer with all the information regarding my attempts to resolve the issue with AliExpress. At that stage AliExpress chose to give me full refund.
Bottom line is, dealing with AliExpress is intentionally frustrating and slow by design. In the first instance the intent is to make you give up and absorb the loss. In the second instance, it is so that your time limit for a charge back is exceeded. My advice would be to gather just enough evidence to clearly show that the package has not been delivered, give AliExpress an opportunity to refund you in full and if they fail to do so, tell them you will initiate a charge back with the credit card issuer. If they do not refund at that stage, contact your credit card issuer, ask for charge back and supply them with your evidence, including a log of your attempts to resolve the issue with AliExpress.