"If you call to reschedule an appointment they..."

My GP referred me to see a specialist at St Thomas hospital. I received a voicemail message saying that an appointment appointment was scheduled for me. Because I wasn't unable to attend that date I called back to reschedule. The receptionist/secretary over the phone treated me with a very impolite manner. They seems to be annoyed by my request and was not keen on offering me few options. Now it is not my fault if I work and if I need to find available time to attend without disrupting my work activity. I underline that this was the first time that I was calling for this matter and I tried to be very quick and decided regarding my availability btw I found this service very poor and irrespectful. I hope I will change my mind the day of my consultation.