In addition to the idea of therapy mentioned by the previous poster, it sounds as though this child needs firmer boundaries. What he doesn’t need is emotional pleas and rational discussions. Instead, focus on taking action. First of all, make sure that he can’t get his hands on your credit cards. But if he does, as soon as you get word that he has made a purchase, you should immediately find him and force him to return it. Right away. If it can’t be done right away, then he needs to surrender the merchandise to you right away. Also, if you are paying for his cellphone or any other extras that aren’t really necessary, then those privileges should be stripped away. Teach him how to treat you (and others) through action, not lectures. Remain calm when discussing misbehaviors. You’re human, so you don’t have to act cheerful when you’re upset, but keep your emotional reaction with him to a minimum. It distracts his attention away from the behavior that you’re trying to help him change.
Aside from that, give him lots of love and positive attention when you can. Good luck to you!