Hi my parcel EB762404888CN shows that my parcel was held/to be inspected by Customs, and then it was returned from Customs. Will this mean part of my parcel was seized and returned back to the seller?

I purchased a duvet set from an English retailer that I was unaware was to be delivered from China. The goods arrived on 28.4.24 and were unsuitable. I, therefore, returned the items by Royal Mail on 7 May 24 and have been tracking and chasing ever since. The parcel has not yet been returned to the supplier, being stuck in Customs in Souzhou. I now know that I should have been advised by the Post Office that a completed customs form should have been attached to the parcel, which it was not as unaware. I suspect this is why the parcel is still noted as held in customs when I track it. My problem is how do I rectify this with Chinese customs to enable return and refund to the supply. Any advice/help very gratefully received please.

Customs says:
shippment left processing centre, AU then my suburb
AU customs clearance completed, returned to overseas warehouse.
How can do I find out where this item is? has it been returned to China?
Tracking number:AM463182889CN
Please advise where parcel is located as it has not been delivered to me.