Attack! Send him a box of chit. Not right away, wait a few months. Mail it when you are out of town so the post mark won't trace back.
Get a cheap calling card and awake him at 3am. Add spice to it. "Charlie get out of there, your house is on fire!"
etc...
Write a letter to his local hospital requesting general info. Use the letterhead on the response to inform him of his son's successful sex change operation.
One cannot rest until revenge 1,000 times over is extracted. Your peace of mind requires a response.