Rubbish collectors demanding money (Kuala Lumpur)

Can someone please explain to me why every now and then rubbish collectors come to the door and demand money? My husband has handled it until today, when I heard someone yelling over my wall. Like an idiot I went to the gate and asked what they wanted. They showed a government issued badge and the guy said he was a rubbish collector and was looking for a donation. I told him I had no money and he replied that he'd be back tomorrow at the same time, so I could have money. Is this payment an obligation or a donation? He made it sound like I had no choice. Can't say I like being bothered; the dogs weren't too impressed either.