Repeatedly calling me and hanging up.
I called it back and it just rings out or automatically disconnects

Caller: Unknown

They called but then hang up when I answered.
Tried calling back but it just keeps me waiting saying, "your call is important" but doesn't say who they are.

Numerous calls as soon as I answered they hung up.

Nuisance call. Phoned me twice in the last 2 days but didn't leave a message. I tried phoning back from a silent number, as I don't answer calls from numbers I don't recognise and it went straight through to a recorded message saying "your call is important to us, please stay on the line an one of our operators will be with you shortly." After about 30 seconds someone picked up and the line went dead. Have now blocked them.