Well, it is your decision whether to pay the discount, or wait for the Notice to Owner, (is this you ?), and submit your reps again on the same basis as before, namely assisting boarding/alighting. You really do need to supply some collateral to explain why you had to assist your dad, like medical documents or suchlike; they won't cancel the PCN just on your say-so. If you wait for the NtO, you lose the discount option, although if they reject a formal representation they may re-offer it. If you take them to the Traffic Penalty Tribunal, it would be for the full PCN penalty. Assisted board/alight is a well-established ground for cancellation of a PCN, but the person claiming it must provide some proof of the need for providing assistance to the passenger.
