FedEx complaint: Fedex trying to charge me a tax i havent agreed with anyone

I received a parcel i ordered from Spain. I paid delivery to the company. 2 weeks after the delivery, Fedex sends me a letter chraging me 31% of the value of the product (not including delivery services).
I immidiately write to Fedex and tell them thats unaccapetable and to take the parcel back if this is what it takes (i hadnt opened it yet by then). NO ANSWER FOR 2 MONTHS. So I assumed they got the money from the company or absorved the cost.
They have now sold the debt to a parasite company called Control account, which are now charging me even more of course. They never dealt with the complaint. I never hired Fedex, neither they checked with me about this additional cost. There is no way i would have paid the amount of money including the import duty for this product. I already thought i was paying a high price for what it was. Can you help me?