There are a few possibilities but foremost did you tried hard braking to really test out the ABS feature? Try speed up at a safe lane(safetly first la lol) then just hit your brakes hard. Try to feel if there are jerks or rough vibrations on ur brake pedals something similar to that. Then the ABS is working fine, by the same time try notice if the ABS light lit as you hardbraking. Usually it is the sensor connected to the ABS light got dirty and need some cleaning or it has got some problem. Try get a more experienced (i meant on ABS systems mechs) to check it out. They could easily trace if the ABS sensor is out of shape or just dirty. One thing in mind is, ABS system itself will not break down easily so if the mechs told you ur ABS system broken then better double check with other mechs first.