"Alternative means of transport needed"

I regularly attend the eye clinic (once a month)at the Northampton General Hospital and for the past 4 months. My treatment has taken about 2 hours which is acceptable. However, yesterday my appointment was for 1700 hr and the treatment time taken was 4 hours -not including travelling to Higham Ferrers. Due to the fact that I cannot drive to the hospital for treatment I have to rely upon a local Voluntary Organisation for transport - due to the 4 hours wait I had to pay £25.00 which to be honest I cannot afford. Up to 2hours waiting time is charged at £12.50 after that double. Can you please advise me if my treatment time can come within the 2 hours at any time during the day, or have you any alternative means of transport which I could use? I do understand that doctors have emergencies etc, but 4 hours wait is in my opinion excessive. Hoping that we can arrive at a compromise as I do appreciate what is being done for me.