What they do is call you to make sure you have answered and then hangs up. A few days later, they will call again as they know they have the right number and a person to speak to.
Also, it's a ghost / fake number as they want you to believe they are calling from Sydney when it's obviously a call centre in the Philippines.
They sell timeshare from Wyndham Hotels and they will give you a $200 supermarket voucher but you have to sit through a 3 hour presentation in a hot & humid room in a far away location with no access to bottled water and toilets. They also lock the doors so you cannot leave the premises. By the time 3 hours are up, you and/or your partner are tired, sleepy, exhausted, desperate to leave that you sign anything for them.
Do not hand over your credit card or go to their seminar unless you want to part ways with $30,000 of your hard earned money and you can only use the timeshare 1 week of the year for the next 5 years. Most times the dates you want to go is always booked out so that they can sell you more timeshare weeks.