"Covid Vaccine Appointment Availability"

I am unable to make my scheduled appointment, so have been trying to reschedule via the website and by calling for the last week. Despite looking in 5 centres for every day in the next 2 months, multiple times each day, there is nothing available. I have also been advised by the call centre not to cancel the appointment I can't make, just not to turn up. This is contrary to everything I've previously been told about NHS appointments and seems ridiculous that I can't free up my slot for someone else. Perhaps this is why there are no alternative slots available as people are not cancelling? Very poor service which has made me anxious about not ever being able to get a vaccine.