If আপনি want to wish "Happy New বছর " to someone in Greece, then আপনি should say: Kali Hronia.
For "Happy New বছর Day" in Greek আপনি should say "Kali Protohronia".
If your friend is called Manolis অথবা Hristos, his nameday is on December 25 (Christmas day). Wish him "Hronia Polla" (Many Happy Returns) for his nameday.
The same applies if your friend is called Vassilis, Yiannis অথবা Fotis. Vassilis nameday is on January 1, Fotis' nameday is on January 6, Yiannis' nameday is on January 7.
During বড়দিন holiday period, which lasts from December 24 until January 6, plus a couple of weeks past that, it is a custom in Greece to wish "Hronia Polla" to the people আপনি meet. So, if আপনি meet someone in the morning, the proper way to greet him অথবা her is: Kalimera, Hronia Polla! (Good morning, Many Happy Returns).