I challenged one 2 months ago and cancelled. It was at Vauxhall station-2 min max. I told them the truth, customer called and told me that she is disabled and it was going to take some time. I believed them however the did not show. It was cancelled after 8 min wait. I made a short drive around the station and came back if she is there -no. Waited another 2 min. No show. I left. After this explanation they asked to send my licences, both PHV and PCO as well as booking details. I sent them screenshot of Uber booking/cancellation. They accepted and cancelled the PCN.
a bit more detail on this,PcN arrived a few day before I headed to abroad for holiday.Further evidence letter arrived when I am away. Following that letter , They sent another one that they proceed the PCN as I did not send what they asked. When I returned back to the UK I sent all docs they asked, return flight tickets to and from holiday as well as a cover letter that tells the story. Therefore they cancelled the PCN. They are nice chaps!