QLD Ex Using My Phone Number Without Consent - Identity Theft?

It is a form of stalking, but getting assistance from the police will be the problem.

Australia is well behind other countries implementing laws that cover circumstances like yours. The UK has had laws in place for almost 20 years

You could try going to court getting an DVO order, not sure how successful it would be.

Yes, not identity theft so much as harassment. It is a criminal offence to use a phone to threaten, harass or seriously offend somebody - however this would normally refer to situations where the offender themselves is calling or texting you. Not giving out your number to others to do it.

However if someone is using your personal information to stalk, intimidate or harass you, you may be able to apply to the court for an intervention order to keep them from contacting you again.

Short of this and annoying as it is, I would change your number and be really careful who you give it out to. And if you have to contact your ex, only communicate via email or skype.

Depending on the facts in detail,
she could be looking at an offence called (for short) "Use a Carriage Service To Harrass"