If you've forgotten what you said earlier, it's “What was I saying?”.
“What did I say?” has a completely different meaning. It is used when you notice the other person reacting in a strange way, and that question really means “You're reacting strangely, I think this is due to something I said, please explain to me which of my words caused you to react like this and why.” Sometimes the person asking this has genuinely forgotten what they said, but often they do remember but don't understand the reaction (or they're pretending not to).
If you've forgotten what the other person has said, you can ask “What were you saying earlier?” or “What did you say, again?” (or other variations). Neither sentence feels completely natural in this meaning without an adverb, though they aren't actually wrong.
“What did you say?” could also mean that you didn't understand what the person say, and with no other clues that's how I would understand it if I heard it.
— I think that [noise of an airplane going by]
— I'm sorry, what did you say?
When there is no apparent risk of interruption, it can also be a way to express surprise or disagreement with what was said.
— I don't like this painting.
— What did you say? That's my masterpiece! Why are you so unsupportive?
“What were you saying?” works best when there is some other context: “Whew, we got rid of the interruption. Now, what were you saying?” It can also have another meaning: when you've done something that changes the situation, and you think that what the person said no longer applies. It is common to shorten this to “You were saying?”.
— I don't like this painting.
[throws the painting away] — There. You were saying?
The most common phrase is "exact change", so you could say Exact change, please. While "change" is usually applied to coins rather than bills when talking about currency, it is acceptable when talking about the return of excess given during a purchase, "Here's your change."
And it is not always applied politely. This news story tells of a Canadian woman who was fined $219 for not having exact change when riding a bus.
Best Answer
Possible things to say are
or
or
(Thanks to @CopperKettle for the first one!) You will notice that all of these use the present perfect. This is an appropriate choice because the situation of "not being paid" is something that continues from the past to the present.
If you use the present tense "you don't", it sounds like you're talking about a general situation, as though your boss never pays you.