The moment you have paid the fine, you have bcome a consumer and has every right to obtain such information. They should have proper authority to collect such fines, provide a valid receipt and should account it as income in account books,. They should have displayed the boards. I do not know whether it works or not but issue a Regd notice demanding for providing the following information under CP Act as they have collected consideration.
1.CCTV footage showing wrong parking of your vehicle.
2.Display of such boards , demarkating the boundaries and intimation about fine,
3.The extant of such rule and authority to collect such fines.
4.The head under which the fine was accounted.
5.The authority that can decide the facts in the case in case of dispute.