The fact that you're posting this shows at least part of you wants to stop, which is encouraging. In the short term you could try looking at ways to self-harm that aren't expensive and are safer, here's a list of ideas:
https://www.healthline.com/health/mental-health/self-harm-alternatives#harm-minimization. Long-term it really has to be about getting therapy, and rationalizing why you feel the need to do this. Because it sounds like hurting yourself isn't enough for you, and that you have to give yourself lasting damage to be satisfied.
It could be because you deep down hate yourself, and you subconsciously want to destroy yourself as much as possible so that you don't amount to anything good. I used to be like that and would purposefully screw up my life when I was depressed (rage at friends and cut them off, sleep around compulsively with strangers, fail my classes, eat as badly as possible) so I had no chance of recovering. But the truth is you are inherently worth a lot as a human and by extension, so is your body. Even the fact that you don't seem interested in harming others, and that you're concerned about your parents, shows that you care for others and that's a wonderful thing. Try and think about why you have less self-worth, what the root of it is. Possibly it's because other people have made you feel inferior, and you're relying too much on others for your own happiness/self-worth.
Or if you feel so numb in life that only this can make you feel something, try and intensely reflect upon why that is. Why does self-harm work for you, but not boxing, or writing angry letters, or violent video games? Is there anything else you could replace it with? This could be a fun exercise because you can really learn about what makes you tick and what works for you more in general. For me I felt the urge to self-destruct because other people would see that I was suffering and feel guilty. I realized that was counterproductive though because people either stopped caring about me, or (in the case of my family) I made them suffer. I didn't want either of those things, and I realized that it made no sense to self-harm when I can take out anger in healthier ways. It wasn't easy to break the habit but it all started with realizing how irrational it was.
It will be a process, but I believe with the right help you can stop eventually. You're still young and the brain can adapt a lot before your mid-20s.
