"appointment cancellation problems"

I was due to have an appointment this week but have received a letter to say it has been cancelled because the consultant isn't available. The letter said my appointment has been reschedule for October. I think this is such a long time away and I'm worried because the appointment is for a follow up after having knee surgery, and my knee is really giving me some bother so was glad that it was going to be looked at this week.

Because of this I phoned up the department that sent me the letter and they said they can't tell me any more info other than that the consultant isn't available anymore. The person on the phone asked me to wait while they get someone else to talk to me, I waited five minutes and no one came so eventually hung up. 

I don't understand why there ins't another doctor available to look at my knee or why I have to wait so long for my next appointment. I'd had the ambulance booked to take me to the appointment too so I've had to call them up and cancel that.