"I do not have your number."
Translation:Je n'ai pas ton numéro.
So--how many people live in a city is un nombre, correct? Or any time I've performed a mathematical operation, even adding up the bill in a restaurant, I've come up with un nombre. But a digit (or series of them) used for classification / identification = un numéro. (I know I'm repeating what you've said, but just to make sure I get it.) I think that the English distinction between number and numeral (where the latter refers to the quantity as a concept, for mathematical purposes) is not nearly so precise. We tend to use "number" much more widely than the French seem to use either of their words. Thank you for the information!!
"pas... de..." is used to mean "not any" and in the absence of another determiner, like a demonstrative or possessive adjective:
je n'ai pas de numéro = I do not have any number
je n'ai pas ce numéro = I do not have this number
je n'ai pas ton numéro = I do not have your number