SECURITY GUARD ABUSE OF POWER

We were driving in Sandton Drive just off William Nicol corner going to Sandton, the road has two lanes that merges into one lane. Drivers give each other way - right side then left side or the opposite as the road merges into one lane, then it was my turn as the car from the right side had passed through, I moved nicely into the one lane. Few seconds later the car with a name ANCHOR SECURITY came besides me the drivers in that car with security uniform started shouting at me, pointing fingers as if indicating that they wanted to shoot at me. My question is what wrong did I do? if the security operators who are supposed to be protecting the public are the perpetrators of violence.