Hiya Hazard,

Did they say it was a mistake?...clearly what they have sent makes no sense

Even if they did say it was an error over the phone, then they should also send you a revised letter by post to confirm the correction.
I'm afraid I wouldn't trust them if there is any risk they keep that copy of your original letter on file, particularly as it is so far in the future....and that applies to all the NHS not just CHX..

Do also keep trying for a cancellation though.... I have heard elswhere that some folk getting appointments at a few days notice..

Chrissty