The appointment time that CX give you includes a 15minute grace period, say your appointment time is 11:45, the accual consiltation is not booked till 12:00 (15 minutes later), this is incase you are late, have paper work to full out and mainly to allow you time to compose yourself before the consultation.Because I bet if you turn up 5 minutes late, they'll happily cancel your appointment and/or discharge you. That's what our local physio does to people who can't walk and so turn up 5 minutes late.
I agree that they should have contatced you before hand about cancelling, did they give a reason why it was cancelled.
The reason that they give you could also contain the reason why they laft it so late... eg doctor had an emeragancey to attend to.
I'm disabled also and use cruches and sometimes wheelchairs, and i can see what incoveniance it has caused, but there would have been a good excuse for the cancelation.