I have never ceased believing in Santa Claus for a couple of reasons.
1. Saint Nicholas was a real historical figure important in the early Christian Church.
2. I personally know Santa Claus and have seen the joy he brings to children and their parents. ( I have been Santa at our local community center for several years.)
The character of Santa Claus is now mixed up with Father Christmas. Father Christmas is a much older character, possibly Roman from the Saturnalia Festival. But all in all both characters represent joy and giving of oneself not just gifts but love and happiness. So as I hope I do that much of the time, I'd say I still believe in Santa Claus.
All the best :)