Is it wrong to call people in full name?

Ｉ get scolded by my senior this afternoon. The senior is Sook Hui, she owned a fairly top position in Chinese Language Society. She was my former senior too in my previous school SMK(P) Air Panas. Ｉ admit that she is not a nice people at all. When she was in the Science society in my previous school my first impression about her- "she was so arroganｔ＂Ｉ can judge that straight away by looking at her face and the way she talk. I also wondered how she was chosen to hold of the top posts. During chinese society meeting today, we were all busy with the preparation for the Chinese Singing Competition. I had some doubt about the envelope which Kar Yen asked me to do, approach her to ask for consultation. I called :" Low Kar Yen...blablabla.." then Sook Hui turned her head facing me angrily and said :"Do you know that it is very impolite to call people in her full name?" Then, I apologise to her. She added:" you say sorry to her(kar yen) not me!" I thought she was the one who was so mind about 'it'. Anyway then, I asked Kar yen was she so mind about 'it'.. She said:"No." That made me felt a bit guilty about it.