UW268498350CN left China Post system for Serbia on Dec 12.

this kind of parcel starting with U is china post ordinary parcel. China Post will not scan and update its status after it left China. so you can not see new status and know where it is now.

This is a slow and cheap service for low value item. Both China and destination country give very low priority to sort and deliver this kind of parcel. china post ordinary parcel might take 4 to 12 weeks to reach your country.

If your buyer protection is expiring, you should open dispute to paypal/aliexpress for lost parcel refund. Otherwise keep waiting.