Tammy, I wish I could suggest something - I'm coming up short on this one. Brenda makes a good point about stolen red plates - I'd never heard it having been done or stories of such but its all too possible.
Bren - as someone who does stay on island a long time, this is what I do - I take route taxis primarily during the day when I have to (I like to walk from point A to point B whenever possible). When I go out at night I call one of my drivers. As stated above if I happen to be out really late (past midnight) I have a couple of night drivers I can call.
It all works out in my transportation budget and is something I've pretty much always done since I got "hipped" to the route taxi system 15+ years ago. Back then route taxis were 30JMD per person...these days at 100JMD the charter can cost just a little more.