How do you deal with a deadbeat dad?

I have a dad who is a deadbeat. My mom had to put him on child support because of his absence in my life. My dad only came around when he had to pay my support. One time I ask him for a simple computer, and he brought me a faulty computer from a pawn shop. I asked him for a car one time, and at first he brought the car over for shoe & tell. When I ask for it he told me I had to buy it from him? Why do some guys become deadbeats? I’m debating if I should just act like he doesn’t exist and disown him, he’s an useless dad. He can’t even buy simple essentials for me.
How do you deal with a deadbeat dad?
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