Try having hypnotherapy by a qualified person who is registered. It does help. You will probably need a couple of sessions.
There was a boy in my classs that had a terrible habit of biting his nails/skin all the time. I asked him to sit on his hands, and he completely stopped biting his nails. His parents were very aware of what was happening. (His father was the headteacher in the school!) He stopped completely within a few weeks. His mom sent me in a very nice Thank You present for all the effort!
B’Hatzlacha!