If he lives at home with his parents too, I would try to get their name/address/phone and communicate with them; they may be having as much trouble with him as you are and be more than willing to help or have ideas on how to stop their son's behavior toward your daughter. If your daughter has no job/money of her own, I would get a different kind of phone for her that you control instead of her and not give her internet at all unless she needs it for school. If she is not acting responsibly/as an adult, do not treat her with trust/as an adult.