This doesn't surprise me at all and unfortunately I don't think you can do much.
Have you used usps?
Here we have to pay duties, ever, even for supersmall amount and for used/personal goods, example 10 euro of duties and handling for 30$ declared, very frustating.
You should have declared the goods as "returned goods" or similar and with a symbolic value declared.
Try to contact agenzia delle dogane in...