Poor service

I ordered stuff on Shein, well I kept tracking my parcel, on the 5th August 2025, my parcel was delivered by FedEx couriers. A month later I receive an email with an invoice saying I owe FedEx courier fees, I am being kept liable for their negligence, and I am being threatened about lawyers, I am not happy with the service received from them at all, if I order stuff online I know I have to pay for my parcel including courier fees. How did they deliver my parcel without checking if it was paid for, whenever I order I always get an email to pay customs. I really had a bad experience, and I have used their services before. What I hate is being threatened with lawyers after a month.