Excel date format

I take care of a list in excel 2013, in which a group of people continuously feeds data (a sort of archive). One column expects dates in a certain format (year-month-day). I applied data format to the whole column, so that it recognises new inserted data as dates in the desired format. However, excel does not recognise the new data as dates, but as text (and writes them in the form day.month.year). When I check the format of the cell, it still tells me date. Since dates are treated as text, sorting according to dates does not work.
I know how to convert the text into dates, once the data as been inserted (e.g. copy-paste to notepad works), but I would like a solution to prevent this conversion from happening, so I do not have to continuously correct the data newly inserted in the sheet.

Do you have any idea? Thank you for your help!