For a parcel rejected, the common reasons are as follows:
The addressee's address is not correct or not clear, the addressee refused to accept the parcel, or the parcel has no people to pick up and exceeds the retension period.

Here is the tracking result for your parcel:
2016-08-13 13:51 "Exchange Bureau in Guangzhou" has been exported
2016-08-13 13:51 "Exchange Bureau in Guangzhou" return notes (98)
2016-08-13 09:23 "Exchange Bureau in Guangzhou" have been exported to open notes (return)
2016-06-21 16:49 "Exchange Bureau in Guangzhou" import each other (internal transit)
2016-06-20 09:30 "Exchange Bureau in Guangzhou" imports open
2016-06-17 08:42 "Melbourne" have been exported directly
2016-06-17 08:35 Leave the "Melbourne"
2016-06-15 13:33 "Australia" has been accepted

As you see, on June 21, it has been in Guangzhou and it was returned back on August. I think they maintain it for over a month but couldn't get connected to the recipient or the address is not correct, so the delivery was failed. You'd better check the address and contact phone number. They are very important.

I have written the addressee clearly which has no doubt at all. Thank you very much for your valuable time.

Parcel No. CF100995265AU 被退回到澳大利亚的哪个地址？
请告诉我们这个包裹被退回的地址，我们可以再申请澳大利亚的邮局帮助查询。谢谢！

The parcel will be returned to the sender's address you wrote when you sent the parcel.

My address as sender of this Parcel No. CF100995265AU is 82 Bray Street Morphettville SA Australia 5043. Please let me know the time when this parcel is posted to this address.
Thank you very much for your valuable time.

One or two months in general. I find the return time is usually very long.

My mobile number is 0401871608.

Thanks