sorting data in ascending date order

Do you mean that the dates are changing how they are displayed (so 10/8/16 (10 August) is now showing as 8/10/16) or are the dates actually changing (so 10/8/16 still shows the same, but now appears to be 8 October)? I ask because just sorting the data shouldn't change it - the information should remain the same - so it seems that the dates are probably already formatted (incorrectly) as mm/dd/yyyy. If the dates are being entered as text, not as dates, then sorting the data might be converting it to mm/dd/yyyy if your system's date format is incorrectly set to that - have you checked your system date settings?

If it's possible to upload a sample file (with confidential information removed), we can take a better look at this.

When I open your file, all the dates display as dd mm yy (the default date setting on this computer) and they seem to be sorted correctly, so I think it must be your settings. Try to change either:
(1) the formatting of the dates in this file (select the columns > in the 'Number' section, click the down arrow beside where it says 'General' or 'Date' > select 'More number formats' at the bottom > click 'Date' on the left and select the format you want, or click 'Custom' on the left and enter 'dd/mm/yyyy' )
or
(2) your regional settings on your computer (Control Panel > Clock, Language & Region > Change the date, time or number format), or change the formatting of the dates in this file.

If neither of these work, let us know and we can investigate further.