I don’t know how old you are, so maybe my response would be different depending on your age. By NOT responding, you actually WERE responding – responding that you are not going to engage in conversation with them. If you are a bit older than 14, you could have nodded and said hello then walked on and ignored them.
Personally, I have always believed that when a Yid says hello, I should respond with a hello, and move on. It has always worked for me, but not everyone would agree with me, I guess. I do think that reporting to their parents would have been an extreme reaction. So maybe it’s better you did not know who they were. Maybe they thought they recognized you from Shul or somewhere else. In any case, as long as they did not harass or try to intimidate you in any way, let that be the end of it.