My understanding is they only check about 1 in 5 packages due to volume, if they saw something they felt was un- lawful to import it would go back to the seller. If they wanted to extract an import duty you'd think they would mail something to you for the charges to release the package after payment. It could be they are just so overwhelmed with incoming packages that it's just sitting there until they get to it. Have you heard anything back from the vendor?
Found it....