This is doing the rounds on social media and doesn't seem to be a one-off or made up. Lots of people in the 60-64 age group have rung to find they have appointments booked early next week yet haven't yet had their letter through the post. My friend said her husband (in the clinically vulnerable group a couple of weeks ago) only got his letter on Friday for a Saturday appointment. If you fall into this group and haven't had a letter then I would ring today if you can or it seems like there's a risk of appointments being missed next week. The appointments are already allocated on the system, just something seems to have gone wrong in the mail system!
It's 0800 0308013 and select option #2 or 0300 790 6296.