just call yourself and leave this message
"I donít know who you are. I donít know what you want. If you are looking for ransom, I can tell you I donít have money. But what I do have are a very particular set of skills; skills I have acquired over a very long career. Skills that make me a nightmare for people like you. If you return my phone now, thatíll be the end of it. I will not look for you, I will not pursue you. But if you donít, I will look for you, I will find you, and I will kill you."
I did have a passing fantasy of going back to the park today with a knife of some sort, but then I thought that probably wouldn't go down too well when the police come to talk to me later tonight.