There are
more possible realities. You listed the 3 first. There are more options, at least these:
4. You paid the taxes when you bought the stuff. Fedex wants the taxes anyways. They would have kept your extra taxes for themselves in the end.
5. You paid the taxes when you bought the stuff. Fedex wants the taxes anyways. They would have paid the extra taxes. The government kept them because, hey, they trust Fedex.
6. You paid the taxes when you bought the stuff. Fedex wants the taxes anyways. They would have paid the extra taxes. The government kept them but eventually returned them, because some kind of accounting kicked in.
7. You didn't pay the taxes when you bought the stuff. The sender didn't either. Fedex informs the sender and you. Fedex pays out of pocket. The sender pays out of pocket.
Could have happened if you paid:
8. You didn't pay the taxes when you bought the stuff. The sender didn't either. Fedex informs the sender and you. Fedex pays out of pocket. The sender pays out of pocket. You pay out of pocket. Fedex keeps twice the taxes in the end.
9. You didn't pay the taxes when you bought the stuff. The sender didn't either. Fedex informs the sender and you. Fedex pays out of pocket. The sender pays out of pocket. You pay out of pocket. The fed. governemnt keeps triple the taxes.
And many variations I can't think of right now.