can FedEx pay duties on my behalf even if I didn't choose them as courier?

[rafa]

Hi, month ago I bought from EU so legally I have to pay duties , £76. The fact, I selected DHL as courier when I made the order although seller contracted FedEx at the end. Few days after they delivered my parcel, they sent an email highlighting amount to pay is £95 not £76 , so I found out they paid on my behalf adding a disbursement fee.

If I didn't select them as courier and I didn't accept any term and agreements, why they paid on my behalf when there is an online tool for paying VAT?

thanks