Hey Hotaru, I got this girl's number, called her and she's frequently unavailable, what should I do?

Quit calling, and move on.

She's avoiding you. For one reason or another. Don't blame yourself. But don't call her anymore.

If I call a girl, and she can't make a little date and doesn't arrange time for one at a better juncture....well....

It's a sign. Heed it and carry on.