According to the tracking (LZ352695709CN) my item was delivered by Royal Mail on 13th October 2020 but it wasn’t.
Royal Mail say that I have to clam through you as International mail rules mean claims for loss or damage are considered by the postal provider of the country the item was sent from.
This applies regardless of which country the item was last tracked to.
What do I do next?

I would like to ask for your help that the item I sent was originally intended for delivery to Macau S.A.R (Postal box 1089). However, I have been tracking the item for a long time, finally I found the item has been stuck in Ningbo's customs for 20 days. Subsequently, it was sent back to Shanghai customs. As of the latest update on 13-Feb, the item is shown as "sent to carrier." Can you please advise me on the status of the letter?
Actually, I have checked with Royal Mail multiple times, and they have informed me that the item is no longer in their care. The latest update on Royal Mail's tracking platform is from 4-Feb, but this status does not match the information provided by China Post. I am unsure of the current location of my item and would greatly appreciate your assistance in resolving this matter. Can you please help me to clarify where my item is located?
Please note that the item is a letter with dimensions of 22.9cm x 16.2cm and not a parcel. Thank you for your assistance.

I've been waiting for my item to be delivered to me,LV381094525CN,I've been following china post Royal mail,since I brought my item on the 17/12/2021,it's now 18/01/2022,and still no item,even though it says it's left overseas,on my UK Royal mail account,but it's still in carriers hand in china,what is going on,please can someone tell me,