RR574206575PL arrived in Guangzhou customs on Dec 14. It is still waiting for import customs clearance. There might be two possible reasons for the delay:
1)you forgot to write receiver's mobile phone number in the parcel. China Post needs to send a customs clearance code to receiver which allows him/her to make customs clearance online. If this is the case, the receiver needs to call China Post hotline 11185. They will guide him to make customs clearance in person.

2)The receiver doesn't not want to accept the parcel and make customs clearance. This often happens when the parcel is a return for a refund. Many bad sellers often play such game to avoid refund. If this is your case, China Post can't do anything for you. You need open dispute to your marketplace like Amazon,Aliexpress etc, or call your bank to file charge back against fraud.

Recipient is a liar. China Post never ask shipper to contact them. Receiver should have received a text message from China Post (if you have written his mobile number in the parcel). If he didn't get the text message, he needs to call CHina Post hotline 11185. They will guide him to do customs clearance in person in post office.

I think the receiver simply doesn't want to accept the parcel and therefore give you some excuse.

Is it a return for refund? If yes, this is not strange.