Learn English – use “it” to refer the plural noun “the fees”

Quote: My dictionary says prey is an uncountable noun.

I would say take such indications as a general hint. Nevertheless a writer can choose whether he wants to use that word as a collective noun with a singular verb or as word with plural meaning in the sense of all the animals that are prey. In this respect - countable or uncountable - English is flexible and tolerant. You will find this flexibility with almost all nouns that are collective nouns for groups. You can use "police" as a singular when you think of the whole of that organisation and you can use it as a plural noun when you think of the lot of people in the police force.

As Rob K mentions in his answer: In your example A has already defined the context, so "it" is perfectly clear.

However, it is not uncommon to say a pronoun without context, but it is awkward since the listener would not know the reference. You would have to add some further explanation what you mean.

A. I'm sorry, it's completely sold out
B. What are you referring to?
A. The game. It's completely sold out.

I don't think this is unique to English, since it's more about the general quirks of pronouns or any ambiguous part of speech.