You have had a really hard time from some posters on here OP.
Some people are ridiculously and fiercely protective of the NHS, when quite frankly parts of it it can be shit and very poorly organised.
The doctors, surgeons, nurses and other patient facing staff are amazing, but the NHS has been spoilt by those higher up and politicians who don't have a clue what they are doing.
Yanbu to be annoyed and inconvenienced by the appointment change especially with it being short notice. I would feel like just turning up and playing dumb myself, but chances are it would be a waste of my time more than anyone else's.
The NHS isn't doing you a favour, it's paid for by the taxpayer and you are entitled to utilise it.
So what if you were looking forward to the scan, it's an exciting time, as well as nerve wracking wanting to check the baby is ok.
There should be something else in place to deal with emergencies and other patients with short notice needs. Existing appointments shouldn't be compromised. That's unfair and causes more problems if the patient is simply unable to attend the updated appointment. Often appointments are just given without discussion, some patients just can't work like that especially self employed people.
The antenatal clinic I attend is often approx 2 hours behind schedule, and I make no apologies for making my dissatisfaction known.
It isn't the midwives fault. But it's still shit. End of.
Last time I was there, I was kept waiting 1 hour 45 minutes past my appointment time. I had more than enough time to collect my daughter from school based on the original time I was given, and was left stressed rushing like mad as there was nobody else to collect her at short notice.
If I hadn't complained and shown how pissed off I was I would have been kept waiting even longer, or either had to miss the appointment I had waited all that time for which was important and couldn't really be missed (anti D), or left my 4 year old at school with a teacher rightly pissed off at being kept behind.
Just because it's the precious NHS doesn't mean patients should be messed about and expected to rearrange their existing commitments, especially at such short notice.