Date format issue - always USA format

[PushkaCom]

Hello - I have the date-picker inastalled with contact form 7,

The date format is always USA date format...

I have changed my wordpress language to British English, changed my WordPress date format to YY/MM/DD - I have added
dateFormat: 'yy/mm/dd',
to every single localisation file in the JS folder...
I added date date7 date-format:dd/mm/yy as my contact form 7 shortcode
in the
datetimepicker.php
file, i added
private $options = array(
'dateFormat' => 'yy/mm/dd',

and it's still showing USA date format
Day/ month/ year

What more can I possibly do? why is it using USA format, and how do I edit the date format?