"Donut bother if you are an NHS patient"

I received an nhs appointment for this hospital. But when I arrived they told me that it had been cancelled. I had no prior notification that it had been cancelled even though they had my mobile number. The reason given was that they did not treat my Condition. Even though I have had previous treatment at this hospital for the same condition. And I also know other people who have had NHS treatment here for the condition. I have. I waited weeks for this appointment , took time off of work and now have to go back to my doctor to be re- referred and go onto another waiting list. Firstly why was this not checked before I was sent the appointment, Why was I not informed of the cancellation. Why accept NHS patients if you do not take them on.