well as far as i know there are no cameras on round abouts...and on many occasions it so happens that one is forced to cross the red signal especially when one is in the round about and there is a car speeding from behind...
are u sure u were fined crossing a red signal in the roundabout? Maybe the traffic police must have noted your number down then...
anyways...write to the traffic dept and hope they atleast reduce the fine...good luck