You are joking right?

But if you are serious, error is here: But I discover that prices have dropped by 4%

You do not simply drop prices, like that. Why did prices drop? (Price) deflation is just a descriptive name not a moving cause. (Price) deflation is not a knob which someone simple turns up and down.

Now depending on why exactly the prices did drop, and by how much you may be either in or out of luck.