URGENT PLEASE - Visitor / Family visa rejected – No refusal

Good Afternoon,
I appreciate any help or assistance
I have an indefinite leave to remain in UK and my mum was intending to visits me on holiday
She visit me on a yearly basis for the last 6 years!
Nothing changed in her circumstances
Strange thing occurred
First of all my mum is partly blinded and has a difficulty reading documents.
Mum picked her passport as usual from the Visa Centre in Cairo and employee said she was granted visa
On checking her passport before her flight next week to the UK on 24th September there is no sign on the visa
Only a stamp with a date that visa meant to be issued 14th June 2015 and a reference number
No Refusal Letter
I believe that the visas get issued from Abu Dhabi
Over 5 different people checked her passport page by page
All documents are provided correctly and she got over 10 visitor / family visa in that passport alone.
Mum phoned me in distress and I am really lost what to do, please help any advice.

Thank you for reading.