"Appointment letter received after date of appointment"

My mother has been waiting for a gynaecology scan since mid March when she was admitted to hospital as an emergency. Today she received, by post, an appointment at the New Victoria Infirmary, but the appointment was for 3 days ago. The letter was dated a two weeks ago. She failed to get past the automated phone system to a human using the number on the letter to explain what had happened and had to find another phone number for the hospital. On getting through the person on the phone was unsurprised and said their new postal system was problematic. As she has an appointment with a gynaecologist in early May, she is keen the scan is taken and reported on prior to then or that will be a second wasted hospital appointment. My mother is in her eighties and is the main carer for my father who has multiple health problems so worrying about her own health is creating her a lot of anxiety and this fiasco re appointments is not helping.

Could you please assure me and my mother that you will rectify this failed system before anymore NHS resource is wasted?