As far as I can see, you're creating file names Devotion_29_02_2016.html for today.
I don't see you calculating which day in the year current day is. Use DateTime methods for that:
DateTime Structure (System)[
^]
In your particular case:
var dttimne = DateTime.Now;
string FinalHtmlName = String.Format("Devotion{0}.html", dttimne.DateOfYear);
Please accept the solution if it solves your problem and good luck.