In Serbia and Montenegro, the main Church is the Orthodox Church and they still use the old 'Julian' Calendar, which means that Christmas Eve is on 6th January and Christmas Day is on the 7th January!
What is the date of Christmas Day in Serbia?
According to my Serbian friend. Christmas in Serbia marked in January 7th. Also she told me about another date which would be January 13th. It's due differences between Gregorian and Julian calendars. But the main date would be Jan 7th.