They called but did not leave a message.
I tried calling back but no answer first time but answered the 2nd time..
the lady (who spoke with an accent) said that it must have been a wrong number.

I've also had the following numbers call and not leave a message:

0413 154 211 (17th June)
0413 154 251 (14th June)
0413 154 274 (13th June)

It's strange that the first 7 numbers are the same as my number.
hmmmmm a bit sus I think.