I'm talking about the actual quantity being demanded. You're talking about a demand function. They are two different things. I'm talking about a number like 1,500. You're talking about something like a coefficient changing in Q = a - bP.

A demand curve shift does result in a change in quantity demanded. However, there are other things that can result in changes in quantity demanded as well (such as a price ceiling or technological progress resulting in lower prices).

You already agreed that a price ceiling leads to excess demand. That means demand > supply. Yet, the supply curve did not shift either. Again, this is because demand is a point on the demand curve. You're confusing a graph of demand at each price with demand itself.