We (well, the experts like Hippocrates!) need to see the original Parking Charge Notice (PCN - as attached to the car, or served by post?). Although it appears you were in contravention as alleged there may well be 'technical' reasons in either the PCN or the council's handling of the case that mean you can get it cancelled - however, this often involves a trip to the adjudicator with the full PCN cost in play. I think what Hippocrates is getting at is that the council will increase the charge at the wrong time, which is not allowed, and grounds for getting it cancelled.