Being infantilised by my parents

I'm 26 and it seems I can't even make a single decision without consulting them first.

I'm in the process of getting braces, and their first port of call is to talk me out of it. Yes, I had them before (only the 'clear' kind) and I wasn't happy with them, hence this. I couldn't even buy a new bike for my birthday because my dad was like "people will try and steal it from you". I have never had anyone even try stealing my bike off me. If they didn't do it when I was 13, why would they at 26?

Before anyone says "they're just looking out for you":

Is it looking out for me when my mum says "something went wrong in your brain when you were born" in front of me and my dad sits there like nothing happened?

Is it looking out for me when my mum would open post addressed to me?

Is it looking out for me when, when I was on anti-depressants, they'd just tell me to stop because they didn't see the point? Yes there were side-effects and I stopped eventually but I should have made that decision on my own terms.

Is it looking out for me when, when I signed up to an advocacy service, they pleaded with me to tell them I didn't want it because, in their eyes, "they tear families apart"?

I'm tired. I keep thinking I can do self-advocacy but nothing works. Nothing gets through to them. I have tried absolutely everything, I've written stuff out, I've tried to force myself to have a meltdown so they'd listen. I'd start punching myself in the face when I'm angry so they took it seriously.

I can't manage my anger and frustration no matter how much I try. Yet at the same time, I know I wouldn't cope on my own. I can barely cope here.

I'd rather a third party come in and help sort things out but there doesn't appear to be many of those services.