How about this as a the final version? I tried to merge the various comments/versions using stamfordman's template.
Dear Harrow,
I parked briefly in this location to escort my elderly disabled father and unload his shopping into his home and left the parking place as soon as he was safely inside with his shopping, which was the purpose of this trip.
He is physically and cognitively impaired with restricted mobility and at risk of falls (medical evidence enclosed) and needs assistance with daily tasks (including alighting the car, entering the house, carrying shopping).
I invited you to accept the exemption of assisted alighting/unloading in my informal challenge but this was ignored, so I am now formally claiming the exemption(s) in my representations.
As the authority is aware there are numerous allowed appeals at London Tribunals for such assisted alighting or boarding of vulnerable or disabled people to and from premises and where it takes the time needed to do so safely in accordance with their needs. Loading is also exempt.
I did also invite you to use discretion regarding my father’s Blue Badge mishap (which was displayed but likely dislodged by the BB holder while alighting) which would also have given me parking permission, and may have been seen had the CEO checked the side window.
I am certain that neither assisting my father into his house nor unloading the shopping took longer than necessary and therefore submit that whether under the grounds of assisted alighting or unloading, the PCN should be cancelled.
I look forward to your acceptance of my representations.