I like to answer these calls and pretend I'm elderly. I tell them to hold on while I go get my credit card and then I just never come back, as if I'd forgotten. For some reason, they usually don't call again.
Reread that and point out where I said anything different than what you did. They're USING the police department as a way to trick you out of money, i.e., claiming to be collecting for their families, injured officers, etc.,. Got to have some reason to call, bogus charities for the police is this one.