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?

Package not received (AS033335055CN) - tracking states that it cleared US Customs and went to the mail processing center the next day where it then was delivered one hour and nine minutes later. Where is this mail processing center that you think delivered the package to my address?

Regarding parcel: LK650065249us
I sent this about six weeks ago via USPS, and it is just sitting in customs.
Please let me know why it has not been delivered.
I do not speak Chinese, so if you can, please give me the phone number for Shenzhen Customs so I can give it to the recipient of this mail.
Thank you.
-Scott