Sorry for you and all the Belgian fans and fans in other UE countries with the same problem, this is totally unfair, I agree with you. Let's hope we'll not have to face something similar in the future.
If it might be helpful for someone, I post here the reply I received from customer service today:
Thank you for reaching out to us. Glad to assist you today. Good to hear that you received your gift. If your order is shipping outside of the US, you are likely to be charged customs fees (taxes, duties, processing fees, etc.) before delivery can be completed. The shipping charges applied to your order do not include customs fees. For any issues regarding customs or duty fees, please contact your local customs office. These fees cannot be refunded, as they are not charged by us.If you refuse to pay the customs fees when your order arrives, the shipment will be returned.
International Standard orders are tendered to your local post office for final delivery. Please contact customs or your local postal service if your order is delayed, as it may have been held for inspection or duties/taxes. This is applicable to all international shipping methods.
We thank you for your time and patience in the matter. Enjoy your day and be safe.