I have a second job. It's only an hour a night Mon to Fri cleaning. My main job is during the day for 6 hours. An online tax professionals did my tax return this year. I have used them for the last 5 years. This year though I got a bill for $1600 to the ATO. I asked the online tax people what went wrong and they said it's because I had a second job. I asked how do I stop it happening next year and they said to fill out a new TFN form and don't tick the second job box. Is this correct? If not what can I do so I don't have another large tax payable next year?