^ Regardless of whether these people are trying to harass you, I think doing anything in retaliation would be a very ill advised thing to do. You'll just make it worse or get in trouble yourself.

I think the best thing to do is just do your best to ignore them, or at least don't react. I'm sure they'll lose interest eventually.

PS - how did they know you couldn't hear them? Have you been doing stuff back & if so, since when?