"Unacceptable gap between appointments"

As a thyroid out-patient I had an appointment at the beginning of October with a member of Dr Jude's team. I was booked for an ultrasound scan and a follow-up appointment was due 6 weeks later, date to be advised by post. I have had the scan but have had to chase for an appointment. Yesterday I hung on for 15 minutes on 2 separate occasions but failed to speak to anyone. I have today managed to get through but there was no record of me needing an appointment. I have been given a date in 2nd week of January, this being the earliest available. My thyroid levels have not yet been confirmed as stable, and I have still not received details of the scan results for the goitre in my neck. There will have been a gap of 3 months between appointments which I feel is unacceptable.