"Clinic appointment put back 6 months"

My son has been diagnosed type one diabetic 3 years ago. It is normal practice, I believe, to have a six monthly appointment at the hospital. The next one he has booked was mid November. He has just received a letter stating that it has been necessary to change the appointment. It has now been changed to late May 2015...... 6 months down the line. This seems a long time ahead, as he will not have been monitored for over a year at the hospital clinic. It is always so difficult to get or change an appointment, phoning the appointments line, there is no joy.