Not true for every police department. I know for a fact that some due so. Unless you are a representative for the police department then you shouldn't discourage people against reporting something.
Actually, you are wrong. I work for a phone service provider and we have been getting fraudulent calls from this number. However, instead of the 30 seconds of silence and a hang up, we sometimes get someone claiming to be a conferencing customer who forgot his chairman passcode but refuses to give us his company name or his callback #.