Hi. It is going to take a lot of time and patiance to turn the attitude Of Billy around. He has been cage bound for a long time and to him it is the safest place to be.You dont say if Billy has moved house as well as having a new carer.If he has this will only add to his fear and agression. I appreciate that you wish Billy to have a better life but it wont happen anytime soon. Caroline has given good advise. Just keep talking to him and when he is ok with that get closer to the cage untill he is actually showing an interest in you. Then you can offer treats by hand In the meantime you have to be patiant and continue caring for him, food, water ect. At the moment the way to his heart will be food.