There is confusing when you are using data picker, for bootstrap datepicker you have to use following code:-
$( ".datepicker" ).datepicker({
format: 'yyyy-mm-dd'
});
and for jquery datepicker following code must be used:-
$( ".datepicker" ).datepicker({
dateFormat: 'dd-mm-yy'
});
So you must be aware which date picker you are using, that is ultimately solve your issue, Hope this hepls you.