which government department i can make a report that a private car park unreasonable charge the carpark fee?

Answer 1

That would have to be the local community. I would start at the city hall. Most of the private garages are just that, private. They have a license to operate and they get to set their own fees.

If the town offices can offer no assistance, I would write a letter to the local papers. Be sure not to personally attackt the garage or the owner. Just state your feelings and their talk about their excessive fees.