be patient with yourself. I don't think just saying "I won't get angry" or repeating "may I be well and happy" is going to cut it here. The work will have to go a bit deeper than just verbally repeating things, however wholesome. Sounds like you have been through quite alot. Actually I can relate to what you say. I had the same problem when I was a young man. I even punched a few holes in the walls of the dwelling I lived in, a bungalow out the back of my parents' house. Like yourself, I had reason to be unhappy with how my parents had treated me while growing up. It was really difficult at that time, because I was just on the brink of moving away from them, and the emotions, all the pain and the realization of the hurt and injustice that had been done to me, was only just dawning on me properly for the first time. As children we can be blind to what is really going on, but as young adults, we see alot more, and it can really hit us quite hard at first.
In my experience, finding a qualified counsellor
you can both trust and get along with, is really helpful in healing from a difficult childhood. If you don't already have one, I suggest looking for one. And don't let anyone rush you into forgiving your parents sooner that you are able to. For the forgiveness to be real, it has to come from a place of wellbeing within yourself, and that is going to take a bit of work.
Lastly, one strategy I used to use, was to at least smash something that was not of much value, and easily replaced. If your laptop happens to be there when you see red, try to quickly pick something else (and I don't recommend the walls of your dwelling, either...ouch
). The habit of smashing things can get expensive if you're not careful.