Parcel delivery can be tricky here unless you live in town with a proper street address.  You say that the post office refused delivery.  My post office say they will take delivery but most of the couriers will not deliver to a post office.  Your options are to have it delivered to someone you know with a proper postal address (not a PO box) or use MRW and ask if you can collect from their office (use that as the delivery address).  There's a convenient office in Amposta.