Australia has a Do Not Call Register. A telemarketing call (which includes where the purpose is “to offer to supply goods or services” or “to advertise or promote goods or services”) is generally illegal if it is made to a number on the Do Not Call Register. There is an exemption if they submitted the number called to the Register to check if it was listed up to 30 days before the call, and it didn’t come back - so generally complaints are only possible if the number has been on the register for longer than 30 days. Consumers can get listed on the DNCR, and submit complaints if they receive a telemarketing call more than 30 days after listing at https://www.donotcall.gov.au/. The legislation can be read here: https://www.legislation.gov.au/C2006A00088/latest/text

In addition, Australia has commonwealth legislation about processing of personal information (the Privacy Act). However, it currently doesn’t apply to ‘small businesses’ - businesses which made less than $3,000,000 of revenue in the previous financial year, unless they are in the credit reporting, health, or data broking business, or supply to the commonwealth. For organisations the Privacy Act applies to, they are only allowed to use personal information for direct marketing in a few circumstances - they obtained it from a person who would reasonably expect them to use it in those circumstances, and they provide an easy way to opt out, and they haven’t opted out. They can also obtain it from someone else with the person’s consent (or if it is impractical to obtain the consent). If asked, they have to disclose what information they hold, and the source of the data. The text of the Privacy Act can be found here: https://www.legislation.gov.au/C2004A03712/latest/text. The government has announced plans to tighten it up, likely including covering small businesses and increasing penalties.

Disclaimer: IANAL, not intended as legal advice, your individual circumstances might vary, consult a lawyer.