He finally ate today, I decided that I would change the way I defrost the food so I put a rat in a sandwich bag and put hot water in from the tap and left it until the rat was warm and floppy, my boa took it straight away and it was clean, no blood or feces so I decided to try it with the ball. I tried him in the tank but he wouldn't take it so I pulled him out and put him on some news paper on the bed and waved the mouse in front of him and he watched it and smelled it for a good few minutes and then he did a nice big poop. This is the first time I've seen any of his droppings since he stopped eating. Anyway, I put him back in the tank, turned off all the lights and left the mouse on top of his hide. I went back in the room half an hour later to get something and the mouse was gone. I'm guessing he was either constipated or maybe he just didn't like wet food. I will be trying him again on Sunday to see if he wants some more. Thank you all for your patience and advice.