If his new mobile number is not updated in the system, then it will be very weird as in how the MR staff is able to contact him at his new mobile number to arrange for an appointment?
The question now is why MR is keeping 2 sets of numbers.
If his mobile number is updated in the system it does not explain why they have 2 sets of numbers and actually sms him on older number to say installation was delayed.
By right I would pull the number from the account information provided and updated by the subscriber ( centralized database accessed by everyone), instead of asking another colleague whats the number to send the delay sms.
So one of the reasons I can think of is that the number wasn't updated.
If he has already updated then the person doing the sms must be looking at some old printed contact list or some spreadsheet that is outdated.