I called back the number (03) 9491 7901 but the phone just kept ringing

Recvd a few calls from this number. They didnt leave any message. Blocked it.

Answered the call, very hard to hear the caller, said he was from a company in Melbourne doing a survey on the behaviours of Australians and that it would only take 2 minutes. I ended the call

"I did the same.. just kept ringing"

I called back the number (03) 9491 7901 but the phone just continued to ring and no one answered.