I was on a waiting list for something and after months and in increasing pain went private. Thing is, the letter I got from the NHS confirming I was on the list also gave me two ways I could cancel my NHS appointment should I wish to.
Neither of those two ways worked. The website version did not recognise the details (codes) that I had been told to give and the phone number I was given meant I spoke to a person who said 'the pin number does not work' which is what I had told them, and they could not cancel it for me manually. The person on the phone then gave me a 'direct number' which was for a hospital in Manchester (hint, I don't live anywhere near Manchester.... I've just googled and it's close to 250 miles away from where I am). I ended up turning up at my hospital's reception and telling them I no longer needed the appointment and they told me disapprovingly that this was not really how things were done.
The whole thing took weeks in the end by the time I got it sorted..... wasted weeks where my spot could have been freed up.