Caught in the act

Of cheating.
Old table and chairs all cleaned, new seating area in well ventilated corner, all ready to sit down to a game of cards, quick pic to a son and off we go.
Son asks me if his father is cheating. I don't understand until I see his face! The face of a cheat. He thinks its funny.
Recently, in highy inopportune circumstances, he said he had lost his phone and would I ring the number while he walked back to the car to check he hadn't left it there. 
Ok. Ring, ring, ring.......this terrible voice answers the phone telling me that if I want the phone I must give him money and quickly. 
So here I am, feeling a bit poorly, with my sister in law who is feeling worse, for other serious reasons, we don't know what to do when He walks in, with the phone and laughing. It was his voice. He thought it was funny.
He can't help it and neither can our wonderful grandson the Titch who is too grown up to figure in my rants.
 They both just get a kick out of winding people up and having naughty fun.
I will get my revenge sooner or later, if and when I can think of something worthy.
Any suggestions?