They call daily - never leave a message - very annoying

The company behind these phone call is called DTS and here are their details:
Level 1 42 Station St Cheltenham VIC 3192
Principal place of business: Level 1 42 Station St Cheltenham VIC 3192
Holder(s) details:
Holder Name: THE FUNDRAISING CENTRE PTY LTDHolder
Type: Body Corporate
ABN: 72 096 066 910

Why do people bother to call back when these conscienceless pests butt into their lives uninvited and they couldn't be bothered explaining why? It just encourages them to persecute the innocent people whose numbers they've somehow got hold of.
Please, do not answer calls from unknown numbers or this plague of nuisance calls will never stop. And don't call back. If they were legitimate callers and actually wanted to speak to you, they would have had the courtesy to leave a message, wouldn't they?

Caller: A fund-raising centre, on behalf of Bully Zero

Bully Zero’s fundraiser call centre bully me, with their calls

Caller: (02) 8053 9531

Call leave msg, hello hello can you hear me hello can you hear me same womans voice for the dozen calls ive had, was thinking scam to get me to say yes a couple times then scam me for whatever they want, blocked this no as the other ones were but they seem to have multiple numbers to call from

Scam callers. Dont answer. Block caller

I've been getting calls from this number every now and then, nobody talks to me. If it wasn't for your comments, I wouldn't have a clue who contacted me. Why do they bother to call if they don't continue with the conversation? I guess it makes their day.

Caller: JJ

Pestered my husband while I was undergoing surgery. Blocked now!

Caller: Anne Fitzgerald representing Bully Zero

Marketing person continued a very lengthy description of a charity service called Bully Zero. Continued with script even when I tried to interrupt. Gave me three choices: Would I like to provide $150, $250 or $350? Should have hung up. Happy to support selected charities but won't encourage unsolicited calls.

My phone rang a feew times and then they hung up. Only got their number through my CID-I didn't bother to ring back don't waste my money. - don't know who it is.

Rings and never leaves a message! Extremely annoying!

Caller: nuisance call,

they call daily, I have "Guardian" phones, so the caller has to identify themselves before my phone rings, if they don't then the call is stopped but I still get a notification that they have rung. but no annoying calls.

Caller: some supposed charit ...

a real person says hello ...that way they identify if its an answering machine etc... ad then click then a robovoice " hi, i am anne fitzgerald for the blah lah bla ..how are you today? I said Non ambivalent ..and its obviously programmed to respond to a reply and it said " that's good, now ... " but i hung up. :)

Calling mid afternoon, doesn't leave a message.

Caller: Charity Fund raising centre..

They don't answer. They call daily. Bloody nuisance.

Phone almost daily . Never leave a message on answering machine.

Phoned several times now. They never leave a message, and the one time that I answered, they hung up.

Why do these people persist in phoning, despite never being answered?? Apparently, they7 must love listening to answering machines, though messages are never left. Also, they always ring at dinner time, which is the one time that I would never pick up a phone.

Caller: Telemarketer

Fundraiser scam on bullying, did not listen

Called several times to our business - never leaves a message - don't have time for this crap