"Cancellation on a short notice"

My appointment was cancelled on a very short notice (one hour before it should have happened, when I was already on my way to the clinic) via a text message (just as well I checked my phone). When I called the centre, I was told the next available appointment would be in three weeks. There is a reason why people are referred for scans, so why not to fit them in other clinics, or to arrange a cover, instead of cancelling on a short notice and rescheduling by ignoring the previous waiting time...