Phoned back and got a message saying the call had been made on behalf of a charity I had supported previously.

They never leave a msg, but ring and ring.

Yes, more and more charities are wasting our donations making these calls.

Missed call. No msg left

Caller: Supposedly a Charity - unknown

Called my mobile; I ignored the call; No VM left; I called the number from the landline and a very sketchy recording started stating that "...this missed call was from a charity that I have donated to in the past..."
I am not convinced it was a bonafide charity call due to the poor state of the recorded message.