I know you posted this awhile ago but I wanted to add my 2 cents as I’m going through very similar things with my 17yo son. What motivates him? Whatever it is… you tie it to what you want to see him do. The best way to do this is to sit down with him and work on solutions together. He feels valued that he’s getting some input in the process and you are getting that buy in from him because he’s motivated now. I recommend looking at Dr Ross Greene’s website – he has a lot of good information on solving problems and lagging skills with our challenging kids. And I love his motto “Kids do well if they can”.
I’m in the US and we are about to take away my son’s electronics tomorrow for the following 4 weeks while he is in an intensive outpatient therapy program. If he becomes violent , as he has done before, the police will be called, he will go to the ER and he will sit in the crisis unit until an inpatient bed becomes available. We will do this as many times as we need to in order to help him obtain the skills to become a functional adult – hopefully a happy one as well. We have done a huge disservice by threatening to do all of this over the years but rarely ever following through and now we have a kid who can’t go to school consistently and lacks healthy coping skills, plays on his electronics all the time barely coming out of his room to do anything else. His room is disgusting, he fights basic personal hygiene, asking him to empty the dishwasher ends up in World War 3. Its awful – I hope my above suggestion will help you out a little bit. I feel for you and wish you the best