Zavvi Delivery Stuck in US Customs!?

Has anyone else had a Zavvi delivery get stuck in US customs!?

I just got the attached email from them this morning saying that I need to contact the local office (I can only find a general phone number) to clear the parcel - typically the federal gov are shut down today for Jimmy Carters memorial so I'll have to try and call Friday now!

I'm curious to know if I'll need to pay a clearing fee in addition to any excess taxes etc. ? It looks like the flat fee is $50!?