Potential scam, no text, no voicemail, multiple calls from dozens of different mobile numbers following a call with TPG Internet, potential middleman attack or kickback

Caller: Freedom Property Investors

This company, Freedom Property Investors, have harassed me for 5 days straight on 7 different phone numbers. They don't leave a message, and you can call the number back and it's a distinctive engaged signal for all of them. A couple of Australian guys answer and start asking you your name and phone number. I don't know where they got my phone number from. I have been dealing with real estate agents of late so I think one of them has given out my number to get a kickback. It's harassment at it's best. I googled them and they are asking for $3000. Do not answer this number or any of the following numbers:
0488 862 646
0488 862 605
0489 900 313
0485 825 728
0417 476 074
0480 090 246.
I don't know how many numbers they have and how long this is going to go on for. There should be a law against this.