Something like that actually happened to me: FedEx will not listen to you, not care, not even give you a way to raise such a request. If you persist in not paying, this will be sent to debt collection. If you persist in not paying, your credit score will be affected.

There is simply no part of FedEx customer service that would deal with it, or if there is, it's well hidden. Yes you could probably go to court over this, but this is almost certainly not worth the time and money.

Source: spent countless hours dealing with this problem in 2023.