http://track-chinapost.com/result_china.php?order_no=RP754891640CN shows the parcel was sent to airline on oct 19.

China Post will lost control of the parcel after sent to airline. so there will be no update anymore after sent to airline date.

Sent to airline does not mean you will get the parcel very soon. It will keep waiting 5 to 10 days in airline warehouse waiting flight space and another 1 to 4 weeks import customs processing in destination country(speed depending on country). The status will stuck at "sent to airline" during this 2 to 8 weeks period.

Once it passes import customs clearance, Serbia Post will scan and update its new location for China Post database and you will see new status.

If your buyer protection is expiring, open dispute for refund. Otherwise keep waiting.