There isn't much, apart from getting a couple of "connected" buddies to "convince" him to return the money. Retrieving money in this type of situation is extremely difficult by legal means. I've had people try similar stunts with me. Bell owns the receiver and you must give it back to them. The guy who sold it to you is a thief and a crook but I doubt the police or Bell will lay any charges.
Procedures for Buying and Selling of BTV Receivers
Procedures for Buying and Selling of BTV Receivers