Supplier shipped an item from Philippines to Chinese warehouse through post office, EE192621553PH is the tracking number, it says items has been held by Chinese customs, how do I retrieve my items, kindly help, it’s been held for over a week, it contains skin supplements I forms of pills and also glutathione supplements

soo i my parcel stuck in china customs like 10 days can tall what is this
parcel number is:LV326500112CN

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.