1)Talk to the father and let him know your displeasure. Determine how he can rectify the problem or if he won't.
2) If the father is a tard, drunk or just doesn't care, get a lawyer and start determining his assets, where he works etc.
3) When needed, start the slow drip of torture on the kid's family, focusing on the old man.
4) There are other, less conventional ways of dealing with this problem. Asymmetric warfare.