Last week I had the same fine. Once the double line was over, I overtook a lorry. (I knew there were police, guys were flashing headlamps on myway, but I didn't know there was a damn zebra crossing. How would I know it? No board signs at least just before it)
They said they can't fine it, instead it should direct to the court. But later agreed to a fine of 500/= for 'Weradi lesa issara kirima'.
Because of a one brave guy..at least he might be a lawyer (In Anuradhapura district as I heard, correct me) we had a time that no highspeed was fined.. We need more people like that! But careful if u don't have any contacts related to police/ politicians. If not, its better to pay the fine, say f*ck off to them and leave. (Of course say it after u came back to the vehicle and shut the door )