1. I guess you are out of luck, your parcel is back in China from Singapore:

Number: RS375361726CN
Package Status: Alert

Destination Country: Singapore
2017-01-04 01:01 Arrival at Destination Post (Country: CN)
2017-01-03 10:05 Arrival at Processing Center (Country code: CN)
2016-12-31 13:58 Returned to overseas (Country code: CN)
2016-12-28 18:51 Further processing in progress (DBUBD)
2016-12-28 18:48 Address is incomplete
2016-12-28 13:45 Delivery in progress
2016-12-24 04:00 Arrived from overseas (Country code:CN), in transit to next processing centre for delivery

Origin Country: China
2017-01-03 15:45 Guangzhou Exchange Bureau, import each other (internal transit)
2017-01-03 10:05 Exchange Bureau in Guangzhou, has imported opening
2016-12-31 16:36 Singapore has been exported
2016-12-28 18:48 Singapore, the post office throw
2016-12-24 04:00 Singapore Singapore, reaching Exchange Bureau
2016-12-20 13:14 Exchange Bureau in Guangzhou, have been exported directly
2016-12-20 07:42 Exchange Bureau in Guangzhou, have been exported to open
2016-12-19 22:08 Bulk acceptance packet processing center in Guangzhou, left, the next station "Terminal of Guangzhou"
2016-12-19 20:12 Bulk acceptance packet processing center in Guangzhou, has
2016-12-19 19:41 Guangzhou international mail operation Center has been receiving and sending
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2. You should advise the seller that the parcel is coming back to him.

3. Here is another tracking for your parcel:
China Post Register Air Mail Tracking System
Parcel No.RS375361726CN tracking result
2016-12-19 19:41:36.0 Guangzhou international parcel process center received
2016-12-19 20:12:28.0 Guangzhou parcel process center customs scan
2016-12-19 22:08:41.0 leaving Guangzhou parcel process center ，next station Guangzhou Airport
2016-12-20 07:42:32.0 Guangzhou Transit Station export security scan
2016-12-20 13:14:00.0 Guangzhou Transit Station export customs cleared
2016-12-24 04:00:00.0 arrive Singapore Singapore Transit Station
2016-12-28 18:48:00.0 Singapore Post Office attempt delivery
2016-12-31 16:36:00.0 Singapore export customs cleared
2017-01-03 10:05:44.0 Guangzhou Transit Station import customs scan
2017-01-03 15:45:51.0 Guangzhou Transit Station import customs cleared (domestic transit )

Thanks.