Or you could try the opposite.
Silence or laying low -while good, solid advice -could be the response of a guilty party, thereby tacitly admitting you were botting.
Ask yourself -if you were wrongly accused of something so bad as botting, would you leave it be? You'd probably challenge it, hopefully with diginity and decorum, but challenge it or at least carry on as normal nonetheless. I suggest you turn off all bots for quite a while, don't even chance it, for as long as you can handle. A week, two, more -whatever. But do it, and play the game as normal. Go back to that zone, watch YouTube in the background and farm by hand the activity your bot was doing. Meanwhile send that guy a reply along the lines of 'whatever' and say you 'have no idea' what he's talking about. That reply serves two purposes: 1.) it baits the guy into divulging more info about when/where/what he reported you for -from there you can better understand where you went wrong and improve upon should you come out of this and return to botting later and 2.) it makes you look human, should you be investigated.
Don't be confrontational and if you do make a reply, remember less is more. The less words you say the more explaining his curiosity will become of him.
To be honest, it's kind of lucky you were told... it gives you vitals on where you went wrong.
But honestly, read the paragraph above and send a reply and most importantly: go back and play as normal. Don't change IP or anything strange, just do it normal for a while.