Excel Date format changed after upgrading

Hello everyone.

My sister wants to upgrade her laptop, so she gave it mo for upgrading.
I have just upgraded from Windows 7 Pro 64bit to Windows 10 Pro 64bit.

After upgrading, I notice the Date Format in Excel files has been changed.
So When I go into CP/Region I cannot find a Format available to display example 6/11/2016 but 6-11-2016 is available.
Someone has forgotten to add the British Date Format and we are left with US Date Format, but only for this particular d/mm/yyyy format. I have two machines that have this undesirable problem.
This problem does not apply to Windows 10 Home OEM (HP)
How does one overcome this nasty in Windows 10 Pro?
The d-mm-yyyy Date Format is no good for Australia.
I have tried Language set to English (Australia) and English (United Kingdom) with no difference.
I need help with fixing this problem
Help Please.