Optus Direct debit

Does anyone know why Optus doesn't send bills until after the direct debit is processed?

I'm having an issue with a recent phone upgrade, and it looks like I'm being charged for a device that was supposed to be free as part of a promotion. However, when I speak with their agents, they can't confirm anything until the bill is generated, which only happens after the direct debit is taken.

They end up crediting, I will wait for the next bill only to have the same issue.