Don't let your mother's hurtful and incorrect words make you feel as if the appointment being cancelled is something personal. There is a reason for it being cancelled, but it is not something done to be personally hurtful. Something happened that required the cancellation. You don't have to react to it, even though I know it feels bad to you. You can really not like it not have to take any action at all. Maybe you could write more about it, here or in a private journal?