Harassed walking past Sahid Sudirman Building

One evening when I was walking on the sidewalk along Mas Mansyur street to my school’s Annex building, I passed the Sahid Sudirman Center building. There were 3 security guards there (who I presume the job is to check the car at the gate). At that time they didn’t look busy since its was after office hours. After I passed them (just less than 5 meters) they started to whistle and say words that I’m not sure what they’re talking about (I wore moderate clothes-jeans and t-shirt and sneakers and had my backpack on btw). After I was about 10 meters away, they kept whistling, so I turned back and I said to one of them ‘Kenapa? Ada masalah?’ (What? Any problem?’) and they just kept silent, even pretended they didn’t see me by looking elsewhere.
I continued walking and they started to ‘hooooo..’ at me and say aggressive words. I didn’t look back but I gave them both my middle fingers bye.