"Missed appointment due to postal delay"

I received an appointment via Royal Mail for 3rd June & 17th June on the 5th June meaning I missed my appointment on the 3rd.

My GP let me know this went down as a DNA even though I didn’t not know I had an appointment to begin with due to the post. The first appointment was a consultation and the second appointment is a review.

I have tried ringing the provided phone number and extension for 3 days in a row and no one has answered or got back to my voicemail. I feel as if this is really frustrating as I would never miss an appointment. I do not want a DNA on my first appointment and I’d also like the second appointment to be changed so the consultant is aware what the appointment entails as he will be more or less reviewing nothing?

This is really frustrating as I need this issue addressing before the 17th and I can’t get hold of anyone.