We had the same thing happening, weeks of calls with hang up as soon as you answer. Rang Telstra and complained, they blocked this number from being able to call our line.

This number keeps calling between 5 & 6 pm most nights. No one speaks, just hangs up. Getting annoying!!!!

Yes, I get the same thing

5 calls in 13 days, hangs up as soon as we speak.
After looking at this site I phoned Hollows Foundation and was told that it was not one of their numbers.

This number has called 7 times in 3 weeks. No one speaks, just hangs up.