When they make issues about missed appointments, it is usually the financial aspect that is the main problem.
Missed appts cost the NHS millions every month, via a combination of wasted time, admin, staff pay, etc.etc.
And every so often surgerys run campaigns to try to communicate this. In my surgery the sign on the wall flashes up messages saying 'Did you know, every missed appt costs us £xx' and 'If you miss an appointment, you took the time someone else could have used.'
It always makes me smile, because if you are sitting in the waiting room reading those messages, then... guess wot... you turned up, didn't you?'
Please remember you are not personally responsible for this huge financial deficit. That takes many people, in many places, over many days.
All you are responsible for is one missed appointment - and you contacted them, explained and apologised. Job done. Lesson learned. Time to move on.
Me? I have missed one appt 5 years ago (forgot, due to thinking Wednesday was Tuesday) and I have rung up and changed the times and dates in advance on long standing appts at the endo clinic a couple of time because, you know, life happens.
We all know that sometimes we miss buses, and meetings and shopping lists, and wear our socks inside out. That's life.
I expect the surgery have completely forgotten about it, and if someone there ever does bring the subject up, then you can be perfectly justified in giving them a 1000 yard stare and saying 'the cost of my missed appt has just increased - yet again - because you have wasted part of THIS appt discussing it'.